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Knowledge of detailed anatomy of the skull base has allowed considerable progress and advances in surgical techniques. Knowledge of dural, bony, and neurovascular spatial relationships of the trochlear nerve has played a critical role in preventing complications during complex microsurgical and endoscope-assisted transcranial and endoscopic endonasal approaches to the supracerebellar region and middle cranial fossae, and to cavernous sinus, parasellar, and orbital regions. The trochlear nerve is long and thin, and the diplopia caused by its lesion due to imprudent surgical maneuvers can have tremendous effects on the patient. The anatomy of the trochlear nerve has been assessed and examined along its entire course from the midbrain to the orbit, in order to perform a classification, anatomically and clinically oriented, of its segments. The nerve has been divided into five segments according to the areas where it is located: cisternal, tentorial, cavernous, fissural, and orbital.

The P2 bypass is one of the most difficult procedures in cerebrovascular surgery. Creating an anastomosis between the arterial graft and the P2 segment of the posterior cerebral artery is challenging because the P2 segment is located deep and high within the ambient cistern. We describe the application of a skull base technique, mastoidectomy and partial rhomboid drilling of the middle fossa, in order to achieve the anastomosis deep in the ambient cistern without temporal lobe injury. Mastoidectomy with hearing preservation creates a presigmoid space, which enables a presigmoid transtentorial approach to the ambient cistern. After complete skeletonization of the semicircular canals, rhomboid drilling of the middle fossa can be performed, confirming the landmarks of the rhomboid, arcuate eminence, greater superficial petrosal nerve, posterior margin of the third branch of the trigeminal nerve, and petrous margin. Partial rhomboid drilling, in which the posterior half of the rhomboid is drilled away, helps to reduce the requirement for temporal retraction during P2 bypass.

A 55-year-old woman presented with a sudden onset of severe headache. Computed tomography (CT) revealed SAH (grade I according to the Hunt and Hess classification), predominantly in the right ambient cistern. digital subtraction angiography (dsA) demonstrated a posterior communicating artery (pCoA) aneurysm (3.2 × 5.1 mm) (Fig. 1c). This patient had suffered sAH because of rupture of a right pCoA 12 years back (Fig. 1a) and had undergone endovascular treatment. Tungsten mechanical detachable coils (MDS; Balt Extrusion, Montmorency, France) were inserted into the aneurysm, and the occlusion was considered to be greater than 90 % (Fig. 1b). she was discharged and returned to normal life without further angiography. After comparing the dsA images of this presentation and the ones 12 years before, the two aneurysms were the same, but the tungsten coils had disappeared. Cranial CT and plain radiographs did not find high radiopacity in other places. On admission, endovascular embolisation was selected. While the patient was under a general anaesthetic, platinum coils (GDC, Boston Scientific, Fremont, CA, USA) were inserted, including two 4 mm × 10 cm coils, a 4 mm × 6 cm coil and a 2 mm × 3 cm coil. The coils were inserted until aneurysmal circulatory exclusion was achieved (Fig. 1d). Whole blood, serum and urine tungsten levels were assayed. The values were 0.00025, 0.00024 and 0.00018 μg/ ml, respectively. The normal serum value is 0.0002 μg/ml. Liver and renal functions were tested, and they were normal. X-ray scan showed no lung fibrosis or dermatitis. Subsequently, she was discharged with no neurological deficit.

Objective To describe the exposure obtained through six approaches to the perimesencephalic cisterns with an emphasis on exposure of the posterior cerebral artery and its branches. Methods Dissections in 12 hemispheres exposed the crural, ambient, and quadrigeminal cisterns and related segments of the posterior cerebral artery. A Stealth Image Guidance workstation (Medtronic Surgical Navigation Technologies, Louisville, CO) was used to compare the approaches. Results The transsylvian approach exposed the interpeduncular and crural cisterns. The subtemporal approach exposed the interpeduncular and crural cisterns as well as the lower half of the ambient cistern. Temporal lobe retraction and the position of the vein of Labbe limited exposure of the quadrigeminal cistern. Occipital transtentorial and infratentorial supracerebellar approaches exposed the quadrigeminal and lower two-thirds of the ambient cistern. Transchoroidal approaches exposed the posterior third of the crural cistern, the upper two-thirds of the ambient cistern, and the proximal quadrigeminal cistern. Transchoroidal approaches exposed the posterior portion of the P2 segment (P2p) in 9 of 10 hemispheres and were the only approaches that exposed the lateral posterior choroidal arteries and the plexal segment of the anterior choroidal artery. Occipital transtentorial and infratentorial supracerebellar approaches provided access to the P3 segment in all cases and exposed the P2p segment in 4 of 10 hemispheres. The subtemporal approach provided access to the cisternal and crural segments of the anterior choroidal and medial posterior choroidal arteries and exposed the P2p segment in 3 of 10 hemispheres. Conclusion Surgical approaches to lesions of the perimesencephalic cisterns must be tailored to the site of the pathological findings. The most challenging area to expose is the upper half of the ambient cistern, particularly the P2p segment of the posterior cerebral artery.

Hydatid cysts of the posterior fossa are extremely rare. Intracranial hydatid cysts are more common in children and occur more frequently in the supratentorial space. A 7-year-old boy was admitted to the emergency department because of intense headache, nausea, vomiting, and progressive drowsiness that developed within the period of a week. On radiological examination a round, 2.5 × 2.5-cm cystic lesion appeared in the ambient cistern and caused hydrocephalus as a result of extrinsic aqueductal stenosis. The cyst was successfully removed using the puncture, aspiration, irrigation, and resection technique via an infratentorial-supracerebellar approach with the patient in the sitting position. The authors here described an unusual case of a hydatid cyst in the left ambient cistern with hydrocephalus due to extrinsic aqueductal stenosis, which seems to be the first such case in the literature. Hydatid cyst may be considered in the differential diagnosis of arachnoid cysts of the quadrigeminal cistern to determine which surgical procedure to perform and to avoid unexpected complications.

A 21-year-old man developed an ipsilateral fourth nerve palsy, contralateral hemianopia, and contralateral hemisensory deficit as manifestations of a proximal right posterior cerebral artery aneurysm. This unusual constellation of signs reflects the involvement of the structures that run in the ambient cistern. The fourth nerve palsy and homonymous hemianopia are attributed to compression by the aneurysm. The hemisensory loss is ascribed to compromise of thalamoperforate arteries emanating from a thrombosed portion of the aneurysm.

OBJECTIVE: Opening the temporal part of the choroidal fissure (CF) makes it possible to expose the crural cistern, the ambient cistern, and the medial temporal lobe. We examined the microsurgical anatomy and the surgical indications for use of the trans-CF approach. METHODS: The microsurgical anatomy encountered in the trans-CF approach for lesions in and around the ambient cistern was studied in three cadavers. On the basis of these cadaveric studies, the trans-CF approach was used during surgery in three live patients with such lesions. RESULTS: The angiographic “plexal point,” which indicates the entrance of the anterior choroidal artery as it enters the temporal horn of the lateral ventricle, was thought to be a key anatomic landmark of the trans-CF approach. A cortical incision for entry into the temporal horn should be made in the inferior temporal gyrus to minimize the potential damage to the optic radiations and to the speech centers. After the CF is opened posteriorly to the plexal point between the tenia fimbria and the choroid plexus, the posterior cerebral artery (PCA) in the ambient cistern can be observed with minimal caudal retraction of the hippocampus. In this study, surgical procedures using the trans-CF approach were successfully performed on patients with high-positioned P2 aneurysms whose PCA ran close to the plexal point or higher, whose medial temporal arteriovenous malformations were fed mainly by the PCA, and whose tentorial hiatus meningiomas protruded into the temporal horn through the CF, with no resulting postoperative visual or memory disturbances. CONCLUSION: The trans-CF approach is especially useful in surgery for lesions in and around the ambient cistern.

OBJECTIVE: The P2 segment of the posterior cerebral artery has remained a challenging region to expose surgically. We establish a surgical strategy for P2-segment aneurysms. METHODS: Each segment of the posterior cerebral artery was classified according to Zeal and Rhoton's classification. Fourteen of 18 P2-segment aneurysms were surgically treated. The patient's outcome, the aneurysm location, and the surgical procedures were evaluated. A cadaveric study was performed to clarify the surgical view obtained via three different surgical approaches. RESULTS: Nine aneurysms were clipped, two were trapped, one was coated, and one was excised with parent artery reconstruction. Cerebral revascularization techniques were used for three patients. The pterional approach exposed the anterior half of the P2a segment. The subtemporal approach revealed the P2a segment, but its exposure was restricted by its localization in the ambient cistern. Via the occipital interhemispheric transtentorial approach, the P2p segment was visible and could be manipulated. When the posterior half of P2a segment was high on a coronal view of magnetic resonance imaging, it was extremely hard to access via any approach. CONCLUSION: A surgical strategy for the P2 aneurysm can be planned with accurate prediction of the aneurysm location. When the localization of an aneurysm on the posterior half of P2a segment is high, a resection of brain tissue may be required.

Object The basal vein of Rosenthal (BV) courses from the premesencephalic cistern, through the ambient cistern, and terminates in the quadrigeminal cistern. The aim of this study was to describe and quantitate the surgical anatomy of this structure and specifically to provide landmarks for identifying this vessel along its course. These data may be of use, for example, to surgeons using subtemporal operative approaches through regions where this vessel is concealed. Methods The authors examined 15 latex-injected adult cadaveric brains (30 sides) to delineate the morphological characteristics of the BV. Dissections of the BV were then performed and measurements were made between this structure and the tentorial incisura at the anterior, middle, and posterior borders of the lateral midbrain. All specimens were found to have a left and right BV with varying morphological characteristics. The mean distance between the BV and posterior cerebral artery at the midpoint of the lateral midbrain was 16 mm. The BV was always found superomedial to the posterior cerebral artery along the lateral aspect of the midbrain, and the BV ranged in diameter from 1 to 5 mm. The BV drained into the vein of Galen in all but two specimens. The mean distances from the tentorial edge to the BV at the anterior, middle, and posterior borders of the lateral midbrain were 11, 13, and 4 mm, respectively. No statistically significant differences were found when comparing left and right sides or male and female specimens. Conclusions The authors hope that these data will help the neurosurgeon operating near the BV to avoid injury to this important structure.

A 38-year-old male presented with a posterior fossa ependymoma with unusual extension from the cerebellopontine angle to the pineal region. Magnetic resonance imaging clearly demonstrated that these two components were continuous through the right ambient cistern. Computed tomography using a bone algorithm revealed enlargement of the right internal auditory canal. This case suggests that ependymoma can extend anywhere within the subarachnoid space along the path of least resistance.

An 18-year-old man presented with a 1-month history of global headache with lassitude and dyspnoea on exertion. Clinical examination was unremarkable except for pallor and tachycardia. An unenhanced CT of the cranium showed marked hypodensity in the region of the superior sagittal and transverse venous sinuses (figure 1A). The ambient cistern appeared to be effaced on CT. In view of the headache and hypoattenuating venous sinuses on CT, the possibility of thrombosis of …

A 66-year-old man presented with clival chordoma associated with subarachnoid hemorrhage. Computed tomography showed subarachnoid hemorrhage in the right ambient cistern and a well-enhanced tumor in the petroclival region. Surgical exploration performed on the day of admission showed a clot in the tumor. The tumor was totally removed. Histological examination showed hemorrhage between the tumor and the dura. The diagnosis was clival chordoma. Subarachnoid hemorrhage in chordoma seems to occur by spreading of intratumoral hemorrhage into the subarachnoid space due to dural invasion.

A 61-year-old woman presented with aneurysmal subarachnoid hemorrhage (SAH) associated with multiple remote intracerebral hemorrhages (ICHs). She had undergone microsurgical neck clipping for ruptured right middle cerebral artery aneurysm and ventriculo-peritoneal shunting 16 years previously. Computed tomography revealed SAH predominantly in the basal cistern and ambient cistern, in association with multiple ICHs in the bilateral tegmentum of the brain stem and right caudate nucleus. Digital subtraction angiography revealed an aneurysm at the P(1) segment of the left posterior cerebral artery. The ruptured aneurysm was microsurgically clipped via a left subtemporal approach without complications. Simultaneous occurrence of aneurysmal SAH and multiple remote ICHs is rare. The spatial pattern of the ICHs in the present case is apparently unique.

Introduction The resection of petroclival meningiomas presents great neurosurgical challenges. Although multiple surgical approaches have been developed, the retrosigmoid route tends to be used to address tumors that are predominantly located in the posterior fossa. Our modification of the lateral suboccipital retrosigmoid approach with the placement of a tentorial incision yields good visualization of the supratentorial part of the tumor around the midbrain. Methods We treated four patients, one with primary and three with recurrent petroclival meningioma, by our modified approach. After lateral suboccipital craniotomy, the infratentorial part of the tumor was removed after detaching it from the tentorial surface. The cerebellar tentorium was then carefully incised from the supracerebellar angle, taking care not to damage the superior cerebellar artery and trochlear nerve. Results The operative field surrounding the midbrain was widened by this procedure, and safe dissection of the tumor from the brainstem and other neurovascular structures was performed with direct observation of the interface. Conclusions Our approach is a useful modification of the retrosigmoid approach to petroclival meningiomas. It facilitates the safe resection of the supratentorial part of the tumor in the ambient cistern behind the tentorium.

The anatomy of the temporal lobe is reviewed as it relates to surgical resections for epilepsy. The major parenchymal structures are defined, and some mention of their functions is made. The arterial supply and venous drainage for the major regions are described. Pertinent anatomic relationships with surrounding structures in the cavernous sinus, ambient cistern, and sylvian fissure are identified.

Objective Lateral supracerebellar-infratentorial approaches are established for lesions in ambient cistern and posterolateral midbrain, but published surgical experiences do not describe results with this approach in the sitting position. Gravity retraction of the cerebellum opens this surgical corridor and dramatically alters exposure, creating 2 variations of the lateral supracerebellar-infratentorial approach: the supracerebellar-supratrochlear approach and the infratentorial-infratrochlear approach. Methods We reviewed our experience treating cavernous malformations and arteriovenous malformations (AVMs) of the posteroinferior thalamus and posterolateral midbrain by use of supracerebellar-supratrochlear and infratentorial-infratrochlear approaches. Microsurgical technique, clinical data, radiographic features, and neurological outcomes were evaluated. Results During an 11-year surgical experience with 341 cavernous malformation patients and 402 AVM patients, 8 patients were identified, 6 with cavernous malformations and 2 with AVMs. Infratentorial-infratrochlear approaches were used in 4 patients (50%), including 3 with inferolateral midbrain cavernous malformations. Supracerebellar-supratrochlear approaches were used in 4 patients (50%), including 2 with posterior thalamic lesions surfacing on pulvinar. Resections were radiographically complete in all cases. There were no new, permanent neurological deficits, nor were there any medical or surgical complications. There has been no evidence of rebleeding or recurrence. Conclusions Gravity retraction of the cerebellum transforms the lateral supracerebellar-infratentorial approach, enhancing exposure and approach trajectories that can be achieved with patients in prone or lateral positions. The increased upward viewing angle of the supracerebellar-supratrochlear approach accesses the posteroinferior thalamus. The increased downward-viewing angle of the infratentorial-infratrochlear approach accesses cerebellomesencephalic fissure and posterolateral midbrain. These approaches open wide corridors for safe surgical resection of symptomatic cavernous malformations and AVMs.

The aim of this study is to describe microsurgical anatomy and to quantitatively analyze exposure using the posterior subtemporal keyhole (PSK) approach combined with the transchoroidal keyhole (TCK) approach to the ambient cistern.We determined the proper location of craniotomy of such combined keyhole approach on 16 sides of cadaver heads. The PSK approach and the TCK approach were performed in the same minicraniotomy to observe microanatomic features and to quantitatively measure exposure limits of the ambient cistern and related structures using image-guided system.Some superficial and bone landmarks could be used to find the proper location of such combined minicraniotomy. In the PSK approach, the exposure distances of the trigeminal nerve and the anterior portion of the P2 segment (P2a) were 10.02 ± 0.76 mm and 16.32 ± 2.02 mm, respectively. The superior, inferior, anterior, and posterior exposure limit of brainstem from the intersection point of the lateral mesencephalic sulcus and pontomesencephalic sulcus was 7.5 ± 0.19 mm, 11.04 ± 0.27 mm, 15.72 ± 0.52 mm, and 10.16 ± 0.38 mm, respectively. In the TCK approach, the vertical distances between the taenia fimbriae and the lateral geniculate body without and with mild caudal retraction of the hippocampus were 5.28 ± 0.46 mm and 11.18 ± 0.57 mm, respectively. The linear exposure distances of the posterior portion of the P2 segment (P2p) or P3 segment were 12.14 ± 1.88 mm. Except of one case, the P2p could be exposed using the TCK approach. The midpoint of the medial edge of the parahippocampal gyrus on the coronal magnetic resonance images provides landmark to choose the appropriate approach.The PSK combined with the TCK approach can simultaneously expose the lower and upper ambient cistern in a proper minicraniotomy.

Epidermoid cysts may occur simultaneously above and below the tentorium. Eleven patients with involvement of both infra- and supra-tentorial cisterns are presented. In two cases the epidermoid, located mainly in the cerebello-pontine angle, spread into the middle cranial fossa; in three the epidermoid extended from the parasellar cisterns to the posterior cranial fossa; in six patients the epidermoid, enlarging the tentorial notch, occupied extensively both cranial fossae. The surgical approach was influenced both by the experience of the surgeon and by the main extension of the epidermoid. Total removal was feasible in two patients only but only one of the eleven patients had a recurrence of the epidermoid. The long term results appear to be unrelated to the size of the epidermoid and to the choice of approach.

To compare the cross-sectional morphologic features of successive thin-layers and CT images of the basal cistern and its application in the diagnosis and management of acute craniocerebral traumas. Successive thin-layer cross-sectional images of the basal cistern were retrieved from the second Chinese visible human (CVH) data set and observed. A total of 40 healthy volunteers were subjected to 64-slice spiral CT scan of the head, and CT images of the basal cistern were compared with CVH images. A total of 413 patients with acute craniocerebral traumas were subjected to 64-slice spiral CT scan of the head, CT image changes of the basal cistern were observed. Thin-layer cross-sectional images retrieved from the CVH data set clearly displayed the sectional anatomic morphology, morphologic change pattern and important adjacent structures of the basal cistern. The quadrigeminal cistern was pateriform or sellaeform; the suprasellar cistern was hexagonal or pentagonal star-shaped; the ambient cistern encircled both sides of the brainstem like an arc band. CT images of the quadrigeminal and ambient cisterns were similar with their CVH images; however, the morphology of the suprasellar cistern changed substantially. In 413 patients with acute craniocerebral traumas, the basal cistern may be normal, or presented with narrowing, obliteration, shift, hematocele, and pneumatosis. Narrowing or obliteration of the basal cistern occurred mostly at the side of dominant intracranial lesions, and frequently occurred in patients with diffuse axonal injury or combination of SDH + CONT + ICH. Thin-layer cross-sectional images of the basal cistern retrieved from the CVH data set correspond satisfactorily to CT images of the basal cistern. Comparison of the two types of images can provide a sectional anatomic basis for the image identification of acute craniocerebral traumas. A careful observation on the initial CT images of the basal cistern for anatomic morphologic changes will help diagnose acute craniocerebral traumas early, improve the management, and appropriately predict the prognosis of the condition.

Controversy remains concerning the management of patients with cerebellar hemorrhage. In this study the records of 42 patients were reviewed. In 60% of them the signs of brainstem compression and upward transtentorial herniation were found. The level of consciousness was found to be consistent with the radiologic finding of the ambient cistern on the CT scan. Complete compression of the ambient cistern was always associated with coma, a partially compressed ambient cistern with stupor or drowsiness, while a normally shaped ambient cistern was associated with a normal level of consciousness. Immediate surgical decompression of the posterior fossa was life-saving for patients with brainstem compression and upward transtentorial herniation. Mortality was 57% for comatose patients and 9% for drowsy or stuporous patients. Ventriculostomy alone is the treatment of choice in cases with only hydrocephalus without brainstem compression or transtentorial herniation.

Background: The superficial temporal artery (STA) to proximal posterior cerebral artery (PCA) (P2 segment) bypass is one of the most difficult procedures to perform because the proximal PCA is located deep and high within the ambient cistern. STA to proximal PCA bypass is usually performed through a subtemporal approach or posterior transpetrosal approach, and rarely through a transsylvian approach. The aim of this study was to describe the operative technique of STA to proximal PCA bypass through a modified transsylvian approach (anterior temporal approach). Methods: STA to proximal PCA bypass was performed through an anterior temporal approach in three patients with intracranial aneurysm. We describe the details of the surgical technique. Results: The STA was successfully anastomosed to the proximal PCA in all cases. One patient suffered hemiparesis and aphasia due to infarction in the anterior thalamoperforating artery territory. Conclusions: STA to proximal PCA bypass can be performed through an anterior temporal approach in selected patients. We recommend that every precaution, including complete hemostasis, placement of cellulose sponges beneath the recipient artery to elevate the site of the anastomosis, and placement of a continuous drainage tube at the bottom of the operative field to avoid blood contamination during the anastomosis, should be taken to shorten the temporary occlusion time.

OBJECTIVE: Surgical approaches to ambient cistern lesions are complex. We investigated the microanatomy of the transtemporal-transchoroidal fissure approach to the ambient cistern with emphasis on exposure of the posterior cerebral artery. METHODS: Dissections were performed bilaterally in five silicone-injected cadaveric heads. Critical anatomic distances, specifically with reference to the P2 segment of posterior cerebral artery in relation to the inferior choroidal point and P2–P3 junction, were measured with digital calipers. Other landmarks (temporal lobe tip, points from the temporal base to the choroidal fissure) were included for quantitative analysis. RESULTS: The transtemporal-transchoroidal fissure approach provided adequate exposure of the ambient cistern, minimized temporal lobe retraction, and allowed assessment of regional microanatomy. The mean distance from the temporal base to the choroidal fissure measured 18.09 mm (range, 16.9–21.9 mm). The distances from the choroidal fissure to P2 varied at the coronal plane of the inferior choroidal point (mean, 6.96 mm; range, 3.6–12.0 mm) and the P2–P3 junction (mean, 6.02 mm; range, 4.3–6.9 mm), respectively. CONCLUSION: The transtemporal-transchoroidal fissure approach provides a corridor to the ambient cistern and P2–P3 junction while minimizing temporal lobe retraction and avoiding interruption of temporal lobe venous drainage. Because of widely variable vascular anatomy, access to posterior cerebral artery lesions using this approach requires preoperative imaging to identify the specific location of the P2–P3 junction.

OBJECTIVE: To minimize therapeutic morbidity such as cognitive function disturbance and vascular injury to perforating arteries, preoperative functional mapping of the basal temperal lobe functions was performed and the medical temporal lesions were resected via a combined subtemperal and transventricular/transchoroidal fissure approach. METHODS: Twenty-one patients with medial temporal lesions including tumors arteriovenous malformations, and medial temporal lobe epilepsy underwent operation. The neurovascular structures in the ambient cistern were first dissected free from the medial temporal lobe with a conventional subtemporal approach. Then the temporal horn was opened through the basal surface of the temporal lobe. Finally, the ambient cistern was accessed from the temporal horn through the choroidal fissure. In five patients, whose lesions were revealed to be located on the dominant side by preoperative intracarotid amytal administration test (Wada test), functional mapping of the basal temporal lobe language cortex was monitored for 1 week by use of a subdural electrocorticogram grid before the extirpation surgery. The entrance point from the temporal base to the temporal horn was determined by the result of the functional mapping. RESULTS: The lesions were resected safely and completely in all cases. Language and cogritive fonctions were preserved even in patients with the basal language area on the dominant side. CONCLUSION: Surgeons can confirm the importart neuovascular structures from the subtemporal route and from the transtemporal horn route by a combined subtemporal and transventricular/transchoroidal fissure approach. This approach is especially effective for avoiding ischemic complications by allowing direct confirmation of the anterior choroidal and thalamoperforating arteries.

Ambient cistern is an expansion of the subarachnoid space of the brain located between the posterior end of the corpus callosum, thalamus and the superior surface of the cerebellum. It represents the extension of the superior cistern to the midbrain, connecting it to the interpeduncular cistern. Ambient cistern cyst accounts for 20 % of all congenital arachnoid cysts (Sinha S, Brown JI. Childs Nerv Syst 2004 ; 20: 100 – 103). It is rarely detected prenatally, mostly during the third trimester of gestation.

Tumors of the hippocampal and parahippocampal gyrus are not uncommon, nor are lesions of the cerebellopontine and ambient cisterns. Lesions in these areas include astrocytomas, meningiomas, gangliogliomas, hamartomas, neurilemomas, epidermoids, and dermoids. Preoperative imaging is an important tool that can help distinguish lesions, making surgical therapy more targeted and appropriate. The authors report a case of a 41-year-old man with right-sided atypical trigeminal neuralgia and a left ambient cistern abnormality that was radiologically interpreted as a mesial temporal lobe or extramedullary ambient cistern mass lesion. Surgical exploration for biopsy revealed an abnormal posterior fossa anatomy and a parahippocampal herniation into the perimesencephalic cistern. Biopsy confirmed the finding of normal brain.

BACKGROUND Endodermal cysts usually develop in the subdural space in the anterior spinal cord and rarely occur inside the cranium. Most intracranial endodermal cysts develop in the posterior fossa. We report the first case of an endodermal cyst in the quadrigeminal cistern. CASE DESCRIPTION The patient was a 71-year-old man who suffered from gait disturbance for 6 months. Although head computed tomography (CT) scanning 4 years previously did not show any cystic lesion, CT and magnetic resonance imaging (MRI) on admission showed a cystic lesion extending from the quadrigeminal cistern to the right ambient cistern. The cyst was subtotally removed via a suboccipital transtentorial approach. The cyst wall consisted of a layer of columnar epithelium and connective tissue. Based on the results of immunostaining, it was diagnosed as an endodermal cyst. CONCLUSIONS It is possible that the increase of secretion from the cells lining the cyst may have caused a difference in osmotic pressure between the cerebrospinal fluid and the cyst contents, leading to rapid enlargement of the cyst. An endodermal cyst should be removed as completely as possible because its cells have the ability to grow and produce secretions.

A 63 year old woman who fell off her bicycle had a left temporal region head injury with evidence of initial loss of consciousness of 5 minutes and scalp excoriation of that area. On arrival at our hospital 30 minutes later she was alert and oriented. Cranial nerve functions, including extraocular motion and hearing function, were preserved. Pain and temperature sensations of the right side, including her face, showed a 70% decrease compared with the left side; however, position and vibration sensations were normal. Other neurological examinations, including motor function, coordination, and deep tendon reflex, were normal. The patient's only complaints were left temporal headache and right hemihypaesthesia. Brain CT on admission showed a discrete and linear high density at the left ambient cistern without other intracranial lesions. On the next day CT showed an obscure low density lesion at the dorsolateral midbrain in addition to the previous lesion (figure). Brain MRI, taken 3 days later, demonstrated an intraparenchymal lesion, at the surface of the left dorsolateral midbrain in high intensity on a T2 weighted image. …

A 65-year-old woman presenting with chronic headaches and without overt visual symptomatology was found to have herniation of the cuneus gyrus into the superior cerebellar cistern. Only one prior case of idiopathic brain herniation has been described, in which the parahippocampal gyrus herniated into the ambient cistern. In that case a biopsy was performed as the herniation was mistaken for a tumor. We describe the features of idiopathic brain herniation that would mitigate the necessity for undergoing brain biopsy.

A 7-year-old Japanese boy with an intracranial lipoma of the quadrigeminal region and complex partial seizures is reported. Among 28 published patients with lipoma originating in the quadrigeminal plate and ambient cistern, 6 suffered from seizures and 3 were mentally retarded. Our patient's seizures were controlled with carbamazepine.

Intracranial lipomas are uncommon, rarely symptomatic, lesions. Those located in the quadrigeminal plate and ambient cistern account for 13% to 43% of cases and are less symptomatic. Of 37 quadrigeminal plate and ambient cistern lipomas reported in the literature, 15 were diagnosed during life, seven in children.1 We had the opportunity to study an additional case of quadrigeminal plate lipoma in a four year old child, who presented with epilepsy and developed behavioural changes tending towards aggressiveness, which both subsided after surgery. In 1986 the patient presented two episodes of tonic-clonic generalised epileptic seizures associated with fever; the EEG was normal. One year later, although he had benefited from therapy with phenobarbitone, he presented episodes of hypotonia, ataxia, motor incoordination, and confusion. A new EEG study disclosed bilateral paroxistic abnormalities, such as sharp slow waves (figure A). The MRI disclosed a well defined lesion at the level of the left inferior colliculus, which showed a high signal in T1 and low in T2 sequence (figure B). Three months before admission, after the reduction of phenobarbitone dose, the child presented a new tonic-clonic generalised seizure. During the previous two years, his parents had noted …

For maintaining the intracranial buffering capacity against shunt obstruction, we tried to seek the most suitable size of the lateral ventricles in hydrocephalic children. Thirty-seven shunted-hydrocephalic children who required emergent revision of the shunt were analyzed. At the time of shunt obstruction, the lateral ventricle remained small (0.35 or less than 0.35 on the Evans’ index) in 13 patients (Slit-like group), but it enlarged (more than 0.35 on the Evans’ index) in 24 patients (Dilated group). The mean age in the Slit-like group was significantly older than in the Dilated group and there was no patient younger than 3 years in the Slitlike group. Compared with the Dilated group, the Slit-like group showed significantly rapid deterioration into lethargy after shunt obstruction. Also, at the time of obstruction CT scans showed a significantly higher rate of narrowing of the ambient cistern. While the shunt was working well before shunt obstruction, the Evans’ index was less than 0.33 in all patients of the Slit-like group. In conclusion, because small ventricles after shunt strongly suggest the presence of ventricular tautness, the lateral ventricular size should be maintained at more than 0.33 on the Evans’ index in shunted children at an age of 3 or more than 3 years.

Background Surgical extirpation of medial temporal (AVMs) arteriovenous malformations has been one of the most challenging issues in neurosurgery. Yasargil classified mediobasal AVM into four subtypes: amygdala, anterior hippocampal, middle hippocampal, and posterior hippocampal lesions. The lesions around the trigone extending forward to the temporal horn, and medially adjacent to the midbrain, can be referred to as posterior hippocampal AVMs. The therapeutic indications and operative approaches for these lesions remain controversial. Methods Nine patients underwent surgical resection for AVMs of the posterior hippocampus using a laterobasal approach. Results In four patients, AVMs were located chiefly within the lateral ventricle, and the lesions were resected using a laterobasal approach through the occipitotemporal sulcus, or through a hematoma cavity within the fusiform gyrus. Clinical improvement followed the procedure in three of four patients. In the remaining five patients, the nidi were located chiefly within the ambient cistern, extending upward to the basal ganglia. Contralateral hemiparesis occurred in three patients. Two patients showed marked improvement following an initial decline in neurologic status. Conclusions A laterobasal transventricular approach is suitable for ventricular AVMs, whereas only limited exposure can be afforded through a transventricular, transchoroidal fissure route for the AVMs within the ambient cistern. For these lesions, a conventional subtemporal approach to the tentorial incisura is preferable.

Ependymomas usually occur in intraventricular or intraspinal locations. Intracranial extraaxial ependymomas (IEAEs) are very rare. Here, we present an unusual case of an IEAE in 25-year-old man. The patient experienced head trauma two and half years prior to presentation, at which time brain computed tomography (CT) showed only a dense calcification in the left ambient cistern. After two and a half years, follow up brain CT and magnetic resonance imaging depicted interval growth of a calcified mass with cystic change. The tumor was successfully treated surgically, and the pathologic examination confirmed ependymoma. Index terms Extra-Axial Intracranial Ependymoma

We report the case of a 22-year old man with intracranial metallic foreign bodies who presented complaining of a headache. His history of headaches had begun when he was five years old and continued with increasing severity. Six months before hospital admission, nausea and vomiting began to accompany his headache. Computed tomography scan revealed that 2 metallic foreign bodies were located adjacent to the vertex and another was next to the ambient cistern. The location and position of foreign bodies suggested that they were introduced in infancy through the anterior fontanelle before its closure in an unsuccessful homicide attempt. This case is one of the few reported cases combining headache and intracranial foreign bodies and we discuss the relationship between headache and these metallic materials.

A case of cerebral cysticercosis is reported in a 49-year-old female who presented with headache, nausea, and vomiting. Lumbar CSF showed the findings of mild aseptic meningitis. CT scan revealed an enlargement of the left ambient cistern and a small cystic lesion in the left frontal cortex. MRI demonstrated multilobular cysts in the left ambient cistern with enhancement of their capsules, which compressed and distorted the midbrain. The cysts were surgically excised, and histological examination of the specimen disclosed characteristic features of cysticercus with viable larva. An excellent value of MRI in the diagnosis of intracisternal cysticercosis is emphasized.

In exposing deep extracerebral or paraventricular lesions, it sometimes may be preferable to resect a small amount of noneloquent brain tissue rather than retract the brain. This may be the case in carefully selected instances when, in the surgeon's estimate, brain retraction may result in significant parenchymal damage, in aneurysmal rupture, or in damage to important bridging veins. Some surgical approaches involving brain resection have been well described. This technical note discusses the following approaches that, though undoubtedly used by many surgeons sporadically, have received less formal attention: (1) anterior-inferior temporal resection for basilar aneurysms, (2) posterior-inferior temporal resection to approach the posterior incisura and avoid damage to the vein of Labbe, (3) parahippocampal resection to expose the posterior cerebral artery in the ambient cistern, (4) paramedial posterior parietal incision to approach the trigone of the lateral ventricle, (5) parasagittal resection to expose the interhemispheric fissure and avoid damage to bridging veins, (6) cingulate resection for pericallosal aneurysms, and (7) tonsillar resection for aneurysms of the peripheral portion of the posterior-inferior cerebellar arteries.

To the Editor. —I have read with great interest the excellent article by Del Brutto et al 1 regarding the successful medical treatment of a giant subarachnoid cysticercus in four male patients with the use of albendazole. The computed tomographic (CT) and magnetic resonance images were impressive regarding the treatment results in such cases. However, the world experience is limited and the following case report will show the deleterious effect of albendazole treatment in a similar case. Report of a Case. —A 32-year-old woman was admitted because of headache, progressive visual loss, and slight right-sided weakness of 3 months' duration. The neurologic examination disclosed a bilateral optic atrophy and right hemiparesis. A CT scan of the head showed a giant subarachnoid cysticercus in the left sylvian region (Fig 1) and several smaller similar lesions in the suprasellar cistern, left ambient cistern, and both cerebellopontine angle cisterns. An intraparenchymal cysticercus was

A patient who presented with a tumor of the left ambient cistern, a left cerebellopontine angle tumor, and a left orbital tumor causing left hearing loss and left exophthalmos without café au lait spots or cutaneous neurofibromas is described. There was no family history of von Recklinghausen's disease. A cerebellopontine angle tumor removed by a suboccipital craniectomy was an acoustic neurinoma. An ambient cistern tumor was approached through a subtemporal route. A tumor arising from the trigeminal nerve was also a neurinoma. An orbital neurofibroma was excised by a frontal craniotomy with removal of the orbital roof. This rare unilateral association of neurinomas and a neurofibroma on the left side was thought to be a forme fruste of von Recklinghausen's disease, and it could be considered a presentation of a mosaic of von Recklinghausen's disease.

The microsurgical anatomy of the choroidal fissure was examined in 25 cadaveric heads. The choroidal fissure, the site of attachment of the choroid plexus in the lateral ventricle, is located between the fornix and thalamus in the medial part of the lateral ventricle. The choroidal fissure is divided into three parts: (a) a body portion situated in the body of the lateral ventricle between the body of the fornix and the thalamus, (b) an atrial part located in the atrium of the lateral ventricle between the crus of the fornix and the pulvinar, and (c) a temporal part situated in the temporal horn between the fimbria of the fornix and the lower surface of the thalamus. The three parts of the fissure are the thinnest sites in the wall of the lateral ventricle bordering the basal cisterns and the roof of the third ventricle. Opening through the body portion of the choroidal fissure from the lateral ventricle exposes the velum interpositum and third ventricle. Opening through the temporal portion of the choroidal fissure from the temporal horn exposes the structures in the ambient and crural cisterns. Opening through the atrial portion of the fissure from the atrium exposes the quadrigeminal cistern, the pineal region, and the posterior portion of the ambient cistern. The neural, arterial, and venous relationships of each part of the fissure are reviewed. The operative approaches directed through each part of the fissure are also reviewed.

✓ To determine the possible efficacy of distal subarachnoid space shunting in the treatment of hydrocephalus, the brains of dogs with kaolin-induced hydrocephalus were examined histologically to discover the location of the kaolin and the nature of any biological reaction to the foreign substance. Hydrocephalus was produced by the mechanical infusion of a sterile kaolin suspension into the cisterna magna. After sacrifice the brains were removed and sectioned at the upper cervical cord, pontomedullary junction, midbrain, and optic chiasm, then histologically studied and photographed. Kaolin deposition was most notably found ventral to the brain stem, approaching the foramen of Luschka, up to and within the third ventricle. Ventrally, the kaolin and subsequent inflammatory reaction extended from the chiasmatic cistern down throughout the pre-pontine cistern to surround the cervical cord. In these cases, the kaolin was not found in the lateral ventricles, nor did it extend above the basal and ambient cisterns to cause inflammation in the cortical subarachnoid spaces. Due to the failure of the kaolin and any accompanying reaction to reach the cerebral convexities, it can be concluded that these distal spaces are potentially functional and open to cerebrospinal fluid (CSF) flow and absorption. The pathophysiology of kaolin-induced hydrocephalus is then due to the inflammatory obstruction of the CSF pathways, preventing normal bulk CSF flow to the distal subarachnoid spaces of the cerebral hemispheres thus mimicking some forms of human hydrocephalus.

Computerized tomography (CT) features of ruptured cerebral arteriovenous malformations (AVM) were analyzed in 21 cases, whose CT scans were taken within 7 days after the attack. High density areas were seen in all cases, and distributed in 14 cases (66.7%) of the subcortical region, 3 (14.3%) of the basal ganglia, 2 (9.5%) of the corpus callosum, and 2 (9.5%) of the cerebellum. In 12 out of 21 cases (57.1 %), high density areas were combined in the ventricular system. High density areas were also seen in one case, either in the ambient cistern or in the Sylvian fissure, respectively. High density area was never seen in the basal cistern, such as in cases with ruptured intracranial aneurysms. From these CT features of the ruptured cerebral AVM, it should be classified in the intracerebral hemorrhage rather than the subarachnoid hemorrhage group.

A combination of computed tomography and angiography permits accurate detailed evaluation of common lesions of the ambient cistern.