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Arachnoid granulations are hypertrophied arachnoid villi, which extend from the subarachnoid space into the venous system and aid in the passive filtration and reabsorption of cerebrospinal fluid. These macroscopic structures have been described in various locations, with the transverse and sigmoid sinuses seen as normal variants on imaging. Here we present the occurrence of an enlarged arachnoid granulation at the foramen rotundum where a variant intracranial venous sinus was identified during routine dissection. Variations, such as the one described herein, should be recognised by those who operate or interpret images of the skull base.

An arachnoid web is an abnormal formation of the arachnoid membrane in the spinal subarachnoid space that blocks CSF flow and causes syringomyelia. Although the precise mechanism of syrinx formation is unknown, dissection of the arachnoid web shrinks the syrinx and improves symptoms. Precisely determining the location of the arachnoid web is difficult preoperatively, however, because the fine structure generally cannot be visualized in usual MRI sequences. In this report the authors describe 2 cases of arachnoid web in which the web was preoperatively identified using quantitative CSF flow analysis of MRI. By analyzing cardiac-gated phase-contrast cine-mode MRI in multiple axial planes, the authors precisely localized the obstruction of CSF flow on the dorsal side of the spinal cord in both patients. This technique also revealed a 1-way valve-like function of the arachnoid webs. Imaging led to the early diagnosis of myelopathy related to the derangement of CSF flow and allowed the authors to successfully excise the webs through limited surgical exposure.

Object: Intrasacral meningoceles are rare cystic lesions that can cause focal compression within the bony sacral canal. Their mechanisms are poorly understood, but most intrasacral meningoceles appear to be intrasacral extradural cysts caused by arachnoid herniating through a small dural defect in the caudal end of the thecal sac. As opposed to perineural cysts, they are not associated with an exiting nerve root. When symptomatic, they can cause sacral pain or sacral nerve root dysfunction due to local compression., Methods: This is a retrospective series from Boston Children's Hospital. All patients in whom symptomatic intrasacral meningocele that required surgical treatment was diagnosed between May 1994 and March 2011 were included in the study. Spine MRI was the diagnostic modality of choice. All patients underwent sacral exploration, with ligation and obliteration of the cyst. Resected cyst wall was subjected to pathological examination., Results: There were 13 patients (11 boys and 2 girls) who underwent operation for intrasacral meningocele. The median age was 8 years (range 5 months-16 years). The most common presenting symptom was back pain (in 5) often described as deep tail bone pain, followed by urinary incontinence (3) and constipation (2). Three patients had evidence of associated tethered cord on MRI studies. Four patients were asymptomatic and their diagnosis was made following imaging for other reasons; they were surgically treated because of the increasing size of the lesion or association with other congenital lesions. Most patients had symptomatic improvement after surgery., Conclusions: Intrasacral meningoceles are rare lesions that may result from a congenital dural weakness and a resultant arachnoid diverticulum. They present in childhood either incidentally or with symptoms secondary to nerve root compression. Identification of the point of herniation through the dura mater and ligation of the lesion provides cyst cure and resolution of symptoms in most patients.

Arachnoid webs are intradural extramedullary bands of arachnoid tissue that can extend to the pial surface of the spinal cord, causing a focal dorsal indentation of the cord. These webs tend to occur in the upper thoracic spine and may produce a characteristic deformity of the cord that we term the "scalpel sign." We describe 14 patients whose imaging studies demonstrated the scalpel sign. Ten of 13 patients who underwent MR imaging demonstrated T2WI cord signal-intensity changes, and 7 of these patients also demonstrated syringomyelia adjacent to the level of indentation. Seven patients underwent surgery, with 5 demonstrating an arachnoid web as the cause of the dorsal indentation demonstrated on preoperative imaging. Although the webs themselves are rarely demonstrated on imaging, we propose that the scalpel sign is a reliable indicator of their presence and should prompt consideration of surgical lysis, which is potentially curative.

Arachnoid granulation is often found incidentally in the dural sinuses and skull. It may also enlarge the dural sinus or inner table of the skull. We report a 46-year-old woman who presented with occipital headaches and arachnoid granulations in both transverse sinuses and torcular herophili. Neurological examination was normal. Fundoscopic examination, visual fields and acuity were normal. The headache resolved with medical treatment. No intervention for these lesions was planned. The patient was followed up with magnetic resonance imaging studies.

Decompression of the foramen magnum for symptomatic Chiari malformation attends a small but significant risk of infratentorial subdural extra-arachnoid hygroma when an arachnoid-sparing procedure is attempted. We present three cases whereby an arachnoid-sparing procedure was carried out and resulted in infratentorial subdural hygroma and hydrocephalus. The complication was managed by re-exploration of the posterior fossa and wide arachnoidotomy. In cases whereby the decision has been made to open the dura, we recommend routine arachnoidotomy in foramen magnum decompression, avoiding the risks of infratentorial subdural hygroma. In cases where arachnoid-sparing procedures have been attempted and subdural hygroma subsequently develops, we advocate re-exploration of the posterior fossa rather than cerebrospinal fluid diversion.

Aim: Surgery is the treatment of choice for children who had tethered cord syndrome (TCS). However, a detailed technique for the release of spinal cord is not described yet. The aims of this study are to present our series of TCS in children and to focus on the details of surgical technique. MATERIAL and, Methods: Forty-nine children with tethered cord syndrome underwent surgical treatment for the release of spinal cord between 2004 and 2009. The mean age was 4.6 years (2 days-13 years). Twenty (40.8%) patients were female and 29 (59.2%) were male. Among the 49 children, 41 (83.7%) had different spinal malformations and 8 (16.3%) had no associated lesion. Sectioning of the filum terminale, cutting the arachnoid and fibrous bands, protection of the rootlets and correction of the associated malformations was the standard surgical method to release the spinal cord., Results: Neurological improvement was observed in 4 (8.2%) patients, while the neurological status was unchanged in the others. Cerebrospinal fluid fistula was the main complication and was observed in 3 patients. No mortality or neurological deterioration was encountered., Conclusion: Spinal cord release with appropriate technique seems to be beneficial in maintaining neurological functioning in children with TCS.

Arachnoid granulations play a role in CSF drainage. They are primarily located adjacent to cerebral venous sinuses. They may arise on a bony surface causing progressive bony erosion. We report two cases of arachnoid granulations eroding the posterior wall of the temporal bone. The aim of this paper was to illustrate the clinical presentation, and the imaging findings of arachnoid granulation of the posterior wall of the temporal bone. They remain asymptomatic in most cases, but they might cause a communication between the subarachnoid space and mastoid air cells, increasing the risk of bacterial meningitis, subdural empyema, and other intracranial infections. Differential diagnoses are also described, including endolymphatic sac tumours.

A 3-year-old girl presented with a transethmoidal meningoencephalocele manifesting as recurrent rhinorrhea. Initially, she developed meningitis, but after treatment she experienced rhinorrhea. Two months later, she again presented with rhinorrhea. Neuroimaging studies revealed a small protrusion (15 mm x 10 mm) at the roof of the ethmoidal sinus. Nasal endoscopy confirmed the diagnosis of meningoencephalocele. The operative findings revealed a small hole in the left olfactory bulb, which had descended into an enlarged foramen along with the arachnoid membrane. The left olfactory bulb was removed, and the enlarged foramina of the lamina cribrosa were covered with a frontal pericranial flap. The defect in the bone was very small, but contributed to the development of meningitis and leakage of the cerebrospinal fluid. Basal cephalocele should be considered in a patient with recurrent rhinorrhea and intracranial infections, even in the absence of any apparent anomaly.

We report magnetic resonance (MR), computed tomography (CT) and angiographic imaging of an unusual giant arachnoid granulation 7(GAG) in the superior sagittal sinus in a man with headache and vertigo. Intrasinus pressure measurements revealed a significant pressure gradient across the lesion. MR imaging is useful to identify GAG and dural sinus thrombosis, whereas dural sinus pressure measurement in certain cases of GAGs can be used to evaluate the lesion as the cause of the patient's symptoms.

We report magnetic resonance (MR), computed tomography (CT) and angiographic imaging of an unusual giant arachnoid granulation in the superior sagittal sinus in a man with headache and vertigo. Intrasinus pressure measurements revealed a significant pressure gradient across the lesion. MR imaging is useful to identify giant arachnoid granulation and dural sinus thrombosis, whereas dural sinus pressure measurement in certain cases of giant arachnoid granulations can be used to evaluate the lesion as the cause of the patient's symptoms.

Congenital muscular dystrophies with brain malformations, such as muscle-eye-brain disease, exhibit neural ectopias caused by overmigration of neurons. Such overmigration is evident in protein O-mannose beta-1,2-N-acetylglucosaminyltransferase (POMGnT1) knockout mouse, a model of muscle-eye-brain disease, caused by breaches in the pial basement membrane. We hypothesize that breaches in pial basement membrane disrupt the neural-meningeal boundary, resulting in ectopia of meningeal fibroblasts in the cerebral cortex and reactive gliosis. To test this hypothesis, the cerebral cortices of developing and adult POMGnT1 knockout mice were analyzed by immunostaining with cell-specific markers and by electron microscopy. The upper half of the cerebral cortex in the knockout mouse contained increased numbers of fibroblasts closely associated with capillaries. During development of the cerebral cortex in the knockout mice, breaches in pial basement membrane allowed emigration of overmigrated neurons into the developing pia-arachnoid, scattering its mesenchymal cells throughout the diffuse cell zone and resulting in ectopia of mesenchyme-derived fibroblasts in the upper half of the cortex. Glial fibrillary acidic protein (GFAP) immunostaining revealed that the upper half of the cerebral cortex in the knockout also contained increased numbers of cells with morphologies typical of reactive astrocytes compared with the wild type. Moreover, most of the GFAP-positive reactive astrocytes were in close contact with ectopic fibroblasts, suggesting that they were induced by the fibroblasts. Collectively, the data support the hypothesis that the cerebral cortex of POMGnT1 knockout mice is characterized by migration defects leading to disruption of the pia-arachnoid, ectopia of fibroblasts in the cortex, and reactive gliosis., ((c) 2007 Wiley-Liss, Inc.)

Arachnoid cysts are frequent incidental findings on neuroimaging studies and in clinical practice. Theories of their origin, still matter for debate, compose four categories: 1) a ball-valve mechanism; 2) an osmotic gradient between the intra- and extracystic medium; 3) primary malformation of the arachnoid membrane or cerebral lobe agenesis; and 4) fluid hypersecretion by the lining cells of the cyst wall. The cause of cyst enlargement is also debatable, although there is strong controversial evidence supporting the last two theories rather than the former. Brain water homeostasis and its regulatory pathways are weakly understood at the molecular level. In this brief report the authors attempt to add new insights into the pathogenesis of arachnoid cysts by considering aquaporin expression in the cyst wall and discuss possible future research directions and molecular targets.

Arachnoid cysts are developmental anomalies usually diagnosed in childhood. The most important complications of arachnoid cysts are subdural haematomas and hygromas and intracystic haemorrhage. In our case we present a 7-year-old boy whose arachnoid cyst ruptured into the subdural space following a mild head injury and disappeared after draining the subdural haematoma by burr-holes.

Background: We describe the very rare condition of an idiopathic spinal arachnoid malformation associated with syringomyelia (SM) and depicted on preoperative magnetic resonance imaging (MRI) whose features were confirmed at surgery., Case Description: A 34-year-old female suffered from progressive gait impairment because of lower limb palsy and sensory disturbances. MRI demonstrated a bulging membrane at the T6 level that was transversely stretched between the dorsal aspect of the spinal cord and the posterior dura mater. At this level, the spinal cord appeared atrophic and pushed anteriorly against the dura with enlargement of the posterior subarachnoid spaces (SAS) and focal collapse of an associated panmedullar SM. Surgery consisted in releasing the arachnoid malformation and opening the inferior segment of the syringomyelic cavity. Pathological examination revealed a fibro-sclerotic tissue with cellular areas of meningo-endothelial cells. Postoperative neurological status progressively improved but slightly. Three-months and 1 year postoperatively, MRI showed the collapse of the whole SM and restoration of cerebrospinal fluid (CSF) flow at the treated T6 level., Conclusion: Spinal arachnoid malformations associated with SM are very rare and have never been described up to now on MRI. Surgical removal of the causative malformation allows spinal cord decompression and prevents the recurrence of the SM by restoring normal CSF circulation.

Object: The literature contains scant data regarding variations in anatomy at the level of the foramen of Magendie in patients with Chiari I malformation and syringomyelia., Methods: Based on their operative experience and hospital data, the authors detailed the incidence of arachnoid veils found in juxtaposition to the foramen of Magendie in patients with hindbrain herniation. Additionally, radiological studies were retrospectively reviewed in cases in which such an anomaly was noted intraoperatively. Of 140 patients with Chiari I malformation who underwent decompressive surgery, an associated syrinx was demonstrated in 80 (57%). The foramen of Magendie was obstructed by an arachnoid veil in 10 (12.5%) of these patients; once the lesion was punctured, the cerebrospinal fluid drained freely from this median aperture. On retrospective review of imaging studies, none of these anomalous structures was evident. In all patients with an arachnoid veil and syringomyelia resolution of syringomyelia was revealed on postoperative imaging., Conclusions: In the absence of a clear pathophysiology of syrinx production, the authors would recommend that patients with syringomyelia and Chiari I malformation undergo duraplasty so that, if present, these veils can be fenestrated.

Arachnoid cysts form a cavity containing a cerebrospinal-like fluid, the wall of which is composed of arachnoidal cells. Other types of intracranial cysts have been described, they differ from arachnoid cysts by the histological characteristics of their wall. To analyze homogeneous series, it is thus necessary to differentiate arachnoid cysts from the other types of cysts. Several localizations of these lesions have been described: the most frequent being the temporo-sylvian area. Arachnoid cysts are considered as resulting from congenital malformations that can change during postnatal life. They can no longer be considered as resulting from cerebral atrophy. This arachnoid malformation could be the primary event or be explained by an impairment of the cerebrospinal fluid drainage generated by venous agenesis. Several mechanisms could account for the inflation of these cysts: secretion by the cells forming the cyst walls, unidirectional valve, liquid movements secondary to pulsations of the veins.

Terminal myelocystocele is a rare form of occult spinal dysraphism in which the hydromyelic caudal spinal cord and the subarachnoid space are hemiated through a posterior spina bifida. A 1.5 month old boy presented with a large lumbosacral mass and urinary incontinence. The magnetic resonance imaging, operative findings and pathological findings revealed a low lying conus with a dilated central canal dorsally attached to the subcutaneous tissue. Ventral subarachnoid space was enlarged and herniated through the laminar defect of the sacrum. The lesion was typical of a terminal myelocystocele. The clinical features are different from those of myelomeningocele in many aspects. Though the incidence is low, terminal myelocystocele should be included in the differential diagnosis of congenital lesions presenting as a lumbosacral mass.

We report three cases of masses within the cerebral dural venous sinuses shown with either MR or angiography. The dural venous sinuses of 10 patients without known venous disease were examined at autopsy. In two patients, three giant arachnoid granulations were identified. On the basis of the literature and our limited autopsy series, we suggest that these lesions identified at imaging are giant arachnoid granulations, normal variants of no known clinical significance.

Based on a macro- and microscopic analysis of the material of 2 section cases and 29 biopsies of persons operated on for arachnoidal cysts two types of cysts were distinguished: 1) arachnoidal cysts that occurred as a result of isolated congenital pathology of the leptomeninx; 2) cysts representing a manifestation of the combined developmental abnormality of the CNS occurring in the form of arachnoidal cysts coupled with intracerebral ones and with pathology of the adjacent cortical parts in the form of gross impairment of its architectonics and developmental abnormality of cerebral vessels.

Cerebrospinal fluid (CSF) physiology, and the pathophysiology of hydrocephalus is briefly reviewed, with emphasis on the arachnoid villae and the CSF-venous interface. Five cases of benign "external hydrocephalus" are recorded and the literature of similar cases is reviewed. It is proposed that anatomical or functional obstruction of various etiologies at the level of the arachnoid villae accounts for the dilated subarachnoid pathways in these patients.

Three cases of cerebellar vermis agenesis are reported and the relevant literature (19 other cases) is reviewed. Other posterior fossa malformations, such as a mega-cisterna magna, arachnoid cyst and Dandy-Walker syndrome, are discussed both from the pathological and clinical view point. We put forward a hypothesis that agenesis of the cerebellar vermis and Dandy-Walker syndrome could be regarded as two different stages of the same malformation.

The radiographic appearances in 14 cases with arachnoid pouches are reviewed. Their clinical summaries, operative findings and anatomical distribution are tabulated.

Thirteen cases of posterior fossa arachnoid cyst are described. Presenting features were usually headache, vomiting, lethargy, and delayed development in infants. Association with congenital defects is sometimes noted. The cysts are considered to result from abnormalities occurring in foetal life.

The reliability of cranial computed tomography (CT) in detecting a broad range of intracerebral disorders has been well established (1) and its complementary role with other neuroradiologic procedures has been documented (2). Some attempts at inferring specific histologic diagnosis from static CT scans have been made (3,4). However, other investigators have demonstrated that it is difficult to separate cystic from noncystic, benign from malignant, and neoplastic from non-neoplastic lesions by absorption coefficients alone (5,6). While initial studies utilizing dynamic CT scanning indicate that patterns of contrast accumulation may be helpful in distinguishing enhancing cerebral lesions (7,16), the differential diagnosis of the low-attenuation lesion remains difficult (17). We present a series of hypodense lesions in the middle cranial fossa that demonstrate a broad range of pathologic entities. Their CT features, differential diagnosis, and pathologic correlation are discussed.

Report on two cases of spontaneous, intermittent and long lasting spinal fluid rhinorrhea. The lesion responsible of the spinal fluid fistula is a glio-arachnoid expansion of the convexity of the frontal pole, contained into a fibrous pedicle ; it crosses the dura mater and penetrates, through a well individualized bone orifice, into the posterior wall of the frontal sinus or into an ethmoid-frontal cell. This arachnoid diverticle is not associated with an hydrocephalon. In the absence of any traumatic past history, its congenital nature may be admitted. No para-clinical investigation makes possible to detect such a minor abnormity ; the isotopic transit of the spinal fluid may remain silent, when performed at a moment of drying up of the nasal flow. Surgical exploratory study of the anterior level has to be complete, while numerous independent diverticles may coexist.

Three case of central arachnoid pouches or cysts which are freely in communication with the subarachnoid space and cause hydrocephalus are reported. One case died; the second recovered following transtentorial opening of a huge cystic cavity located between the tentorium and the cerebellum, which opened into the cisterna magna. The patient was well although mentally retarded 6 years later. The third case was treated with a ventriculoatrial shunt and has fully recovered. In these cases, the shape and situation of the pouches are consistent with a processes of upward movement of CSF. In the CSF waves, originating from constant variations of venous pressure, there is an obvious aetiological factor. Even if the hydrocephalus were primary and the pouch secondary, the pouch might contribute to the progression of the former by occasional compression of the aqueduct. This can be another example of the way hydrocephalus leads to its own exacerbation.

In spite of modern instrumentation that is widely available, inaccurate and even crude techniques are still occasionally used for puncturing cavities within the cranial cavity. Thus, a standardized technique for intracranial puncturing, based on stereotaxy, is suggested and illustrated by some clinical cases.

A child with hydrocephalus treated by a valved shunt was reinvestigated after developing a shunt infection. A pouch was discovered invaginating the floor of the third ventricle and filling slowly with CSF from the region of the interpeduncular cistern. Histology and mechanisms of this pouch formation are discussed.

In 11 cases of intracranial, temporal arachnoid cysts the etiology, clinical and radiographic findings, surgical treatment, and outcome are reviewed in respect of post-traumatic subdural hematoma. Cysts of the middle cranial fossa are susceptible to trauma, which may cause bleeding either into the cyst or into the subdural space. Signs and symptoms of increasing intracranial pressure (ICP), local neurological deficits, and sometimes epileptic seizures may lead to hospitalization. CT or MRI scans are diagnostic in these cases. In cases of intracranial mass lesion with displacement of the midline structures and increasing ICP, osteoplastic craniotomy is performed and the lateral wall of the cyst is resected down to the tentorial notch by a microsurgical procedure, with opening into the basal cisterns. There were no operative or postoperative complications in 11 consecutive cases. However, one boy required a cystoperitoneal shunt 3 months later as a result of hydrocephalus following subdural hematoma. Asymptomatic arachnoid cysts are discussed with respect to brain function and social behavior.

The authors discuss reabsorption of cerebrospinal fluid in relation to the post-mortem findings in two children, one with total agenesis of the Pacchionian system accompanied by hydrocephalus, and the other with a subtotal agenesis and no hydrocephalus. Case 1 is the only known documented case of total agenesis of the Pacchionian system and gives credence to the idea that an impaired reabsorption of cerebrospinal fluid at the level of the Pacchionian system is a cause of hydrocephalus. The patient in Case 2 showed only two small areas of arachnoid granulations containing a few flattened, microscopic villi of normal cellularity.

Eight cases of intracranial arachnoid cysts are reported. They are benign congenital lesions who result from an abnormal development of the earliest arachnoid. A subsequent development is possible. The macrocephaly is the first sign and other symptoms give evidence to the localization. Thanks to the C.T. scan one can make the diagnosis, appraise the repercussion and put the therapeutic indications. The surgical treatment is reserved to symptomatic forms. The peritoneal shunt takes the ablation's place. This method is easier and less liable to complications. The results depend on the localization, the pattern of operation and the precocity of the diagnosis.

Two cases of post-traumatic extradural hematoma complicating an arachnoid cyst of the middle cranial fossa in children are described. While subdural and intracystic hemorrhages are well-known complications from this malformation, the association with extradural hematoma has never been previously reported in the literature. The pathogenetic mechanisms are discussed and the particular vulnerability of intracranial arachnoid cysts is stressed.

The typical appearances of middle foss arachnoid malformations as seen by computed tomography, are presented in six cases out of 3700 unselected CT scans performed in the last two years. These lesions have well-defined borders, the anterior border often conforming to the configuration of the greater sphenoid wing, and the posterior border merging into the Sylvian fissure medially. They exhibit the same attenuation coefficients as cerebrospinal fluid (CSF), in the range of 0 to +8 EMI units. Their size is variable. They produce less mass effect than might be expected, even when their size is considerable. Their appearance does not change after infusion of contrast material. Although arachnoid malformations occur in many intracranial sites, the site of predilection appears to be the middle cranial fossa. The clinical presentation and subsequent management of the six cases is briefly described. The pathogenesis and common clincial presentation associated with these lesions is discussed.

Two children with congenital ocular motor apraxia (C-OMA) associated with congenital malformations of the central nervous system (CNS) are presented, and the literature is reviewed. C-OMA is an abnormality of ocular motility characterized by defective or absent voluntary horizontal gaze, associated with a characteristic head thrust. Although not rare, it is infrequently recognized. C-OMA is not a specific disease entity, but a sign. It may be associated with other static congenital CNS disorders and must be distinguished from acquired ocular motor apraxias (A-OMA) seen in progressive brain disorders and in certain serious systemic diseases. Therefore, when movements typical of C-OMA are observed, a careful systemic and neurologic examination should be performed, including immunoglobulin screening, cranial computerized tomography scanning, and adequate follow-up. Close relatives also should be examined.