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Background: The etiology of enlarged subarachnoid spaces of infancy is unknown; however, there is radiologic similarity with normal pressure hydrocephalus. Adults with normal pressure hydrocephalus have been shown to have altered cerebrospinal (CSF) flow through the cerebral aqueduct., Objective: To explore potential similarity between enlarged subarachnoid spaces of infancy and normal pressure hydrocephalus, we compared MRI-measured CSF flow through the cerebral aqueduct in infants with enlarged subarachnoid spaces of infancy to infants with normal brain MRIs., Materials and Methods: This was an IRB approved retrospective study. Clinical brain MRI examinations including axial T2 imaging and phase contrast through the aqueduct were reviewed for infants with enlarged subarachnoid spaces of infancy and for infants with a qualitatively normal brain MRI. The brain and CSF volumes were segmented using a semi-automatic technique (Analyze 12.0) and CSF flow parameters were measured (cvi42, 5.14). All data was assessed for significant differences while controlling for age and sex using analysis of covariance (ANCOVA)., Results: Twenty-two patients with enlarged subarachnoid spaces (mean age 9.0 months, 19 males) and 15 patients with normal brain MRI (mean age 18.9 months, 8 females) were included. Volumes of the subarachnoid space (P < 0.001), lateral (P < 0.001), and third ventricles (P < 0.001) were significantly larger in infants with enlarged subarachnoid spaces of infancy. Aqueductal stroke volume significantly increased with age (P = 0.005), regardless of group., Conclusion: CSF volumes were significantly larger in infants with enlarged subarachnoid spaces of infancy versus infants with a normal MRI; however, there was no significant difference in CSF flow parameters between the two groups., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In infants without a history of trauma, subdural haemorrhages should raise the concern for an abusive head injury, particularly when they are associated with bridging vein clotting/rupture or with septations. However, non-haemorrhagic, fluid-appearing subdural collections (also called hygromas) may also be the result of abuse. Subdural collections have also been uncommonly observed in patients with benign enlargement of the subarachnoid spaces (BESS) and a few large-scale studies accurately investigate the incidence and the significance. Currently, there is a wide variation of practices in children with BESS and subdural collections. Due to the social risks associated with abuse evaluation and the perceived risk of radiation exposure, there might be a reluctance to fully evaluate these children in some centres. The diagnosis of physical abuse cannot be substantiated nor safely excluded in infants with BESS and subdural collection(s), without investigation for concomitant traumatic findings. The exact prevalence of occult injuries and abuse in these infants is unknown. In macrocephalic infants with subdural collections and imaging features of BESS, thorough investigations for abuse are warranted and paediatricians should consider performing full skeletal surveys even when fundoscopy, social work consult, and detailed clinical evaluation are unremarkable., (© 2023. The Author(s).)

Idiopathic syringomyelia (IS) and refractory syringomyelia (RS) are types of syringomyelia that often pose a management challenge and are associated with long-term clinical sequela. They are usually an epiphenomenon reflecting an underlying pathology where the treatment of the primary cause should be the aim for any surgical intervention. In the case of IS, the initial step is agreeing on the definition of the terms idiopathic and syringomyelia. After a rigorous exhaustive clinic-radiological workup, only IS patients with progressive neurology are treated, usually unblocking subarachnoid cerebrospinal fluid (CSF) pathway obstruction somewhere in the thoracic spinal canal and reserving shunting techniques to nonresponsive cases. Similar to IS, also RS is multifactorial, and its management varies based on the initial pathology, strongly supported by radiological and clinical features. We aim to address this topic focusing on the etiopathology, investigation paradigm, and surgical pathway, formulating algorithms of management with available evidence in literature. Surgical techniques are discussed in detail., (© 2022. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

Objective: Computed tomography (CT) of the brain can allow rapid assessment of intracranial pathology after traumatic brain injury (TBI). Frequently in paediatric TBI, CT imaging can fail to display the classical features of severe brain injury with raised intracranial pressure. The objective of this study was to determine early CT brain features that influence intracranial or systemic physiological trends following paediatric TBI., Materials and Methods: Thirty-three patients (mean age, 10 years; range, 0.5-16) admitted between 2002 and 2015 were used for the current analysis. Presence of petechial haemorrhages, basal cistern compression, subarachnoid blood, midline shift and extra-axial masses on the initial trauma CT head were assessed. ICP and arterial blood pressure (ABP) were then monitored continuously with an intraparenchymal microtransducer and an indwelling arterial line. Pressure monitors were connected to bedside computers running ICM+ software. Pressure reactivity was determined as the moving correlation between 30, 10-s averages of ABP and ICP (PRx). The mean ICP, ABP, cerebral perfusion pressure (CPP; ABP minus ICP) and PRx were calculated for the whole monitoring period for each patient., Results: The presence of subarachnoid blood was related to higher ICP, higher ABP and a trend toward higher PRx. Smaller basal cisterns were related to increased ICP (R = -0.42, p = 0.02), impaired PRx (R = -0.5, p = 0.003). The presence of an extra-axial mass was associated with deranged PRx (-0.02 vs. 0.41, p = 0.003) and a trend toward higher ICP (14 vs. 40, p = 0.07). Interestingly the degree of midline shift was not related to ICP or PRx., Conclusions: The size of the basal cisterns, the presence of subarachnoid blood or an extra-axial mass are all related to disturbed ICP and pressure reactivity in this paediatric TBI cohort. Patients with these features are ideal candidates for invasive multimodal monitoring.

Background: Migration of the bullet within the spinal subarachnoid space has long been recognized as unusual complication of spinal gunshot injury., Objective: We report a case of migratory low velocity intradural lumbosacral spinal bullet causing cauda equina syndrome. The relevant literature is reviewed and all cases of migratory spinal bullet are summarised, and management strategies are discussed., Study Design: Literature review., Methods: A 32-year-old male suffered abdominal gunshot injury for which emergency laparotomy and repair of colonic perforation were performed. The bullet was seen lodged within the sacral spinal canal behind the S1 vertebral body. The probable entry point was at L2-L3 level. Caudal migration of the bullet within the spinal subarachnoid space leads to the appearance of cauda equina syndrome., Results: Bullet was retrieved following upper sacral and lower lumbar laminectomy. Prone positioning of the patient had lead to cranial migration of the bullet at L4 level which was confirmed on fluoroscopy. Laminectomy had to be extended upwards with the patient in reverse Trendelenburg position for bullet removal., Conclusions: Caudal migration of the bullet within the lumbosacral subarachnoid space results in cauda equina syndrome. Surgical retrieval of the bullet ensures the early recovery of neurological symptoms. Prone patient positioning can influence bullet location. Intraoperative fluoroscopy prior to skin incision is essential in addition to preoperative imaging to locate the bullet and thus avoid incorrect lower level laminectomy. Trapping the bullet after durotomy using suction and dissector in reverse Trendelenburg position is a useful aid in bullet removal.

Introduction: External lumbar drainage (ELD) of cerebrospinal fluid (CSF) in posttraumatic refractory intracranial hypertension (ICHT) is controversial. We report our experience of ELD in ICHT associated with acute disturbance of CSF flow within subarachnoid spaces (SASs)., Materials and Methods: Four adult patients admitted to the neurointensive care unit for severe TBI who presented with secondary ICHT are retrospectively reported. When refractory to second-tier therapy, if external ventricular drainage were not possible or failed, and in the absence of an indication for craniotomy to treat a mass lesion or decompressive craniectomy, we assessed the evolution of CSF volume within cranial SAS and checked the presence of basal cisterns and the absence of tonsillar herniation to evaluate interest in and the safety of ELD., Results: As second-tier therapy failed to lower intracranial pressure (ICP; mean ICP 37 ± 5 mmHg), and computed tomography (CT) showed abnormally enlarged cranial SAS following traumatic subarachnoid hemorrhage, patients received ELD. ICP decreased, with immediate and long-term effect (mean ICP 5 mmHg ± 2 mmHg). There were no complications to report., Discussion: Acute traumatic external hydrocephalus may explain some of the specific situations of secondary increased ICP, with a "normal" CT scan, that is refractory to medical treatment. In these situations, lumbar drainage should be considered to be a safe, minimally invasive, and effective surgical option.

Idiopathic normal-pressure hydrocephalus (iNPH) has become socially significant in Japan. Japanese guidelines for iNPH in 2011 described the diagnostic importance of "disproportionately enlarged subarachnoid space hydrocephalus" (DESH) on magnetic resonance imaging (MRI). However, some patients with iNPH have equivocal or no features of DESH. To clarify the diversity of MRI findings in iNPH, we classified iNPH into three types based on MRI findings. Using this, we investigate predictable MRI findings for shunt effectiveness in iNPH. A total of 83 patients with suspected iNPH who were treated with shunt surgery were reviewed in this study. All patients had a positive cerebrospinal fluid (CSF) tap test. Among the 83 patients, DESH was noted in 64 %, incomplete DESH in 23 %, and no DESH in 13 % (see Fig. 3). Among the three types of incomplete DESH, incomplete DESH-v (ventricle) was 0 %, DESH-c (convexity) in 13 %, and DESH-s (Sylvian fissure) in 10 %. A high improvement rate after the shunt surgery was noted in the DESH and incomplete DESH-s groups, showing 73.5 % and 87.5 %, respectively. The non-DESH group showed a fairly large improvement of 63.6 %. A common MRI finding in DESH and incomplete DESH-s was high convexity tightness with ventriculomegaly. This combination was promising for shunt effectiveness in patients with suspected iNPH. Further study is necessary to elucidate the pathogenesis.

The recently introduced rabbit blood shunt subarachnoid haemorrhage model is based on the two standard procedures of subclavian artery cannulation and transcutaneous cisterna magna puncture. An extracorporeal shunt placed in between the arterial system and the subarachnoid space allows examiner-independent SAH in a closed cranium. Despite its straightforwardness, it is worth examining some specific features and characteristics of the model. We outline technical considerations to successfully perform the model with minimal mortality and morbidity. In addition, we discuss outcome measures, advantages and limitations, and the applicability of the model for the study of early brain injury and delayed cerebral vasospasm after SAH.

The authors describe a case of 28-year-old man who presented with cervical myelopathy and lumbar radiculopathy due to the giant cervical pseudomeningocele extending to the lumbar spine at 10 years after previous brachial plexus injury. To evaluate the communicating tract between pseudomeningocele and subarachnoidal space, the multidetector-row helical CT with simultaneous myelography was performed preoperatively. The surgical treatment in the cervical spine included the resection of pseudomeningocele and the repair of dural defects communicating into the cyst following multi-level laminoplasty and foraminotomies. At 6 years after surgery, the significant neurologic recovery and complete obliteration of cysts in the whole spine area were maintained. This serves as the first report describing the significant neurologic recovery after the surgical treatment of giant cervical pseudomeningocele extending to the lumbar spine after previous brachial plexus injury.

Objective: To evaluate the relevance of exposure and host biological factors in the heterogeneity of the clinical, radiological and inflammatory picture of neurocysticercosis (NCC)., Methods: 105 Mexican symptomatic NCC patients confirmed by imaging were studied before they received any specific treatment. The relationships studied were those between a) the patients' characteristics (gender, age and level of exposure), b) the type of clinical picture and c) the radiological and inflammatory characteristics of the disease (number, aspect, localization of the parasites, and CSF leukocyte counts)., Results: Seizures were the most frequent symptom and multiple subarachnoid cysticerci the most frequent localization. Symptomatology related to the developmental stage, number and localization of the parasites as well as the CSF leukocyte-counts. The total number of cysticercal lesions and of vesicular cysticerci increased with age,whereas the number of colloidal cysticerci decreased. CSF leukocyte-counts were higher in women than in men. Levels of exposure did not correlate with the clinical and radiological pictures., Conclusions: The variability found in the number, stage, localization and inflammation in the parasite lesions is strongly associated with the heterogeneity of NCC symptoms. The increased number of vesicular cysticerci and the decreased number of degenerating cysticerci with aging, as well as the prominence of inflammation in women suggest that immuno-endocrinological factors may play a role in susceptibility and pathogenesis. The data also show that with increasing age and exposure there is no increment in severity, a suggestion that there might be ways of regulating pathogenicity.

Purpose: The role of subarachnoid blood and secondary, sterile inflammation in the pathogenesis of posthemorrhagic hydrocephalus (PHH) is not well understood. The aims of this study were to study the frequency and rate of spread of blood into the spinal subarachnoid space (SSS) and to evaluate the relationship of this finding and PHH., Materials and Methods: Nine premature babies with major intracerebral hemorrhage (ICH, grade 3 or higher), and ten premature infants with minor ICH (grade 1) or no evidence of ICH (control group) were identified and underwent serial cranial and spinal sonography at the time of initial diagnosis, 12-24 h after the ICH and weekly thereafter for at least 9 weeks. Sagittal and axial scans of the thoracolumbar spine were obtained and evaluated for the presence of echogenic debris in the dorsal SSS. Six additional patients who had cranial and spinal sonography died within the 1st week of life and underwent post-mortem examinations., Results: The SSS was echo-free (normal) in all cases at the time of initial sonographic diagnosis of ICH. Within 24 h, all babies with major ICH had developed increased echogenicity of the cervical and thoracic SSS. Echogenicity of the SSS decreased gradually over several weeks. Although transient ventricular dilatation was present in every patient, only one patient had rapidly progressive PHH requiring shunt placement. Transient cysts of the cervicothoracic subarachnoid space were identified in two patients 6-7 weeks after ICH. The subarachnoid space remained echo-free in all control infants At autopsy, all four infants with echogenic spinal debris had blood or blood products in the spinal subarachnoid space, whereas two infants with echo-free spinal images did not., Conclusions: Spread of blood from the ventricular system into the spinal subarachnoid space after ICH is common and can be seen within 24 h of initial ICH. Subarachnoid blood is associated with post-hemorrhagic ventricular dilatation and transient spinal subarachnoid cyst formation.

The subarachnoid position of the microcatheter has an impact on the outcome of continuous spinal anaesthesia (CSA). The present prospective, randomised study investigated the influence of two different spinal needles on the radiographically documented subarachnoid positions of microcatheters in CSA. In addition, the influence of the subarachnoid position of the microcatheter on onset time of analgesia, dose requirement of local anaesthetics, and level of analgesia was examined. METHODS. Forty orthopaedic patients received CSA using a 28-gauge spinal catheter inserted either through a non-directional 22-gauge Quincke needle (group 1) or a directional 22-gauge Sprotte needle (group 2). After initial injection of 2 ml to a maximum of 5 ml of supplemental doses of 0.5% plain bupivacaine, onset time of analgesia at the level of T 10, dose requirement of bupivacaine, and the achieved analgesic level were registered. After surgery, a dye-enhanced AP X-ray film of the lumbar spine was performed for radiological control of the subarachnoid catheter position. RESULTS. There was a higher number of cranial catheter positions in group 2 (60%) compared with group 1 (40%, P = 0.037). In contrast to group 1, with 35% caudally directed catheters, no catheter was seen in a caudal position in group 2. Onset time of analgesia (P = 0.0002) and anaesthetic dose requirement (P = 0.037) were lower in patients with cranially directed catheters compared to patients with the catheters situated at the level of the puncture site or in a caudal position. Maximal analgesic levels were higher in cranially directed catheters compared with other localisations (P = 0.022). CONCLUSIONS. Sprotte needles provide a higher number of cranially directed microcatheters, which are associated with faster onset of analgesia, lower dose requirement of local anaesthetics, and higher analgesic levels in CSA. The results suggest more effectiveness and probably more safety in microcatheter CSA using Sprotte needles for catheter insertion.

The aim of this study was to quantify the intra- and extraventricular cerebrospinal fluid (CSF) spaces in children with benign enlargement of the frontal subarachnoid space (BE). The infra- and supratentorial CSF compartments were measured in 61 CT examinations of children with BE, 3-27 months old, and compared with those of 96 CT examinations considered normal. Measurements of the ventricular system, and the pontine and chiasmatic cisterns were related to cranial size. In all children with BE the lateral and third ventricles were dilated and the chiasmatic cistern was widened. The subarachnoid space was wider than the upper limits in the control group, in the frontal region (4 mm), and the anterior interhemispheric (4 mm) and Sylvian (3 mm) fissures. The infratentorial CSF compartments, the occipital subarachnoid space, the posterior part of the interhemispheric fissure and, in most cases, the cortical sulci were normal in size in children with BE. The majority were macrocephalic or had rapid head growth but there were also normocephalic children with normal head growth. The size of the posterior fossa was within the normal range in all children with BE. Idiopathic BE is not uncommon in children up to about 3 years old who are healthy or have minimal neurological disturbance and is characterised by a specific pattern of widening of the supratentorial CSF compartments.

Delayed post-traumatic erosion of the skull base is reported in three patients who presented as adults with cerebrospinal fluid fistulae and a history of recurrent meningitis. These skull defects were associated with herniation of the subarachnoid space into the diploe of the skull base, the paranasal sinuses and the orbit. This rare complication of head injury is assumed to have occurred as the result of a dural tear at the time of trauma. Its site probably determines whether a resulting meningocele widens the intradiploic space or broaches the cranial floor.

Objective digital determination of CSF spaces is discussed, with ventricular and subarachnoid spaces handled separately. This method avoids the difficulty of visual definition of ventricular borders in planimetric measurements. The principle is to count automatically all pixels corresponding to CSF in a given region with a Hounsfield unit and to multiply this number by the pixel size. This will give the total surface area of CSF spaces in square millimeters. The calculation of pixel values for CSF spaces and brain tissue is experimentally formulated taking the intersection of the Gaussian curves for ventricular content and brain tissue. In practice, the determination of CSF spaces is done by first calculating a histogram of the total brain in a given slice defining all CSF spaces. Next a histogram of a region including ventricles with adjoining tissue is calculated and the ventricular size is calculated. By subtraction of the ventricle value from the total CSF space value, the subarachnoid space size is obtained. The advantages of this method will be discussed.

The chance opacification of the subarachnoid space surrounding the Gasserian ganglion, observed during metrizamide basal cisternography, is reported. This is compared to similar demonstrations of the optic subarachnoid space. Such infrequently observed images should be known because they may be related to the occurrence of trigeminal neuralgia.

In a comparative study between Dimer X and Amipaque (metrizamide) for lumbar myelography it was found that there is a little higher frequency of monor, but unimportant side effects after Amipaque. Amipaque has also been used for thoracocervical myelography with excellent results and without greater discomfort than after myelography in the lumbar region. A new puncture technique was used for the eximation of the cervical region alone: lateral puncture on the neck between the laminae of C1 and C2 under TV control. In more than 75 reinvestigations no arachnoid changes were observed.

A distinct CT enhancement pattern of leptomeningeal metastasis from a systemic malignancy is described, corresponding to the pathologic and myelographic patterns of this entity. The uniform total subarachnoid enhancement, simulating intrathecal contrast, heralded sheetlike tumor proliferation along the surface of the spinal cord in an asymptomatic patient. Since the majority of hypervascular intraspinal abnormalities show focal enhancement with intravenous contrast, recognition of this pattern may provide unique clinical information.

158 pneumoencephalographies of infants less than 2 years old were examined and 53 of them had a large cavum veli interpositi. A neuroradiological description of this cistern is given and a comparison made with injected anatomical specimens. A statistical comparison with 105 pneumoencephalographies without a cavum veli interpositi does not shown any correlation between the presence of this cistern and pathological conditions. This investigation indicates that a large cavum veli interpositi in the newborn has no relation to hydrocephalus or cerebral atrophy. The younger the child, the more frequent is the presence of this cistern, especially under eight months of age.

Metrizamide CT cisternography in a young woman with a chronic sixth nerve palsy demonstrated a cavernous sinus subarachnoid diverticulum originating from the cerebellopontine cistern. The possible etiologic role of this diverticulum in her palsy is discussed.

The CAT scan is insufficient to make the differential diagnosis between an arachnoid cyst and an epidermoid cyst in the cistern of Galen. Gas encephalography is necessary. This procedure reveals arachnoid cysts of the commmunicating type, but is insufficient in distinguishing between an epidermoid cyst and a non-communicating arachnoid cyst. In this situation, histograms of the absorption values in each section of the lesion may be helpful for the diagnosis.

A review was performed of the computed tomograms (CTs) of 500 children which had been reported as showing widening of the supratentorial subarachnoid spaces with normal cerebral substance. On the basis of this a radiological diagnosis of cerebral atrophy had been made in all but five, who were said to have megalencephaly. From these, the children with large or abnormally enlarging heads, but normal or only slightly enlarged ventricles, were selected; there were 40 such cases (8%). The clinical condition either improved or remained stable over a period of 2 years; in the majority the scan abnormality regressed (22.5%) or remained static (67.5%). In three cases there was slight progression of the CT changes before stabilisation, but only one case developed classical communicating hydrocephalus necessitating a shunt procedure. This condition is a generally benign and mild form of communicating hydrocephalus, for which an aetiological factor was apparent in about two-thirds of the cases studied.

Fifty patients underwent myelography with the newly developed CSF-isotonic, dimeric, non-ionic contrast medium Iotrolan. Repeat spinal and cranial computerised tomographic studies with measurement of the attenuation values were conducted to demonstrate the administered contrast medium in the spinal canal and intracranial subarachnoid space. The patients were examined neurologically, observed clinically and asked about concomitant symptoms. The period of retention and the spread of the contrast medium in the subarachnoid space was not found to have any influence on the side effects rate. In particular, no association was confirmed between intracranially demonstrable contrast medium and the occurrence of side effects.

A method for measuring the subarachnoid space by using an independent CT evaluation unit is described. The normal values have been calculated for patients, according to age, and three examples are presented demonstrating reversible decrease of brain volume in patients suffering anorexia nervosa and chronic alcoholism.

In order to check the constancy of convexity block, the airencephalograms (AEG) of seventeen patients who had undergone two separate examinations were reexamined. A satisfactory filling by air of the basal cisterns or Sylvian fissures was a prerequisite for including the AEG in this series. Consistent results related to air filling of the parietal region were obtained at the two examinations except in one patient with clinical signs of a pontine neoplasm. When the AEG was repeated in a very short time and with unchanged clinical conditions, the degree of air filling over the convexity was practically identical. But, with progressive neurological signs, the parietal air blocks showed a slight increase and also extended to the frontal region. It was concluded, firstly, that upper convexity block is a reproducible finding; secondly, that it is related to organic brain disease, the extent of the convexity block being correlated to the degree of clinical deterioration. As judged from other studies using isotope cisternography, the subarachnoid space is usually not complelely obstructed. It is suggested that the organically changed brain and leptomeninges create special physical conditions for the appearance of convexity air block in the AEG.

A case of metastases to the spinal subarachnoidal space from a primary anaplastic pulmonary tumor visualized by Amipaque myelography is reported.

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

Twenty-two patients with dementia were examined by pneumoencephalography using special technic with the aim of filling the subarachnoid convexity space. Seven had no obvious hydrocephalus. All patients had convexity blocks which were more or less extensive. Ten had bilateral air block in the frontal, parietal and occipital regions. It was concluded that convexity air block is not a technical artifact and consequently seems to have an organic background.

The angiographic and high-resolution, thin-section CT appearance of the normal ambient cistern is correlated with anatomic dissections and sections of normal, formalin-fixed cadaver brains. Each of three separate anatomic segments of the ambient cistern--the supratentorial segment, the tentorial edge and the subtentorial segment--has a characteristic CT appearance that can be correlated with specific vascular structures on routine angiography.

The normal ventricular system and subarachnoid space were evaluated on the CT scans of 155 children chosen from 1,400 pediatric CT examinations, and linear measurements were made. The left septum-caudate distance was greater than the right, and the width of the left anterior horn and size of the skull were larger in boys. The interhemispheric and sylvian fissures, the third ventricle and Evans' ratio were larger in the younger group (less than 3 years) than in the older (greater than or equal to 3 years), while the opposite was found for the cella media index and size of the skull. The size of the lateral ventricles (expressed by anterior horn width, septum-caudate distance and width of cella media) was not different in the two age groups of children. Normal limits for the linear measurements and indices are given in Table 2.

A marginal low density area is often revealed by CT scan in infants with microcephalia. However, it is difficult to assess precisely the main pathologic state of the marginal low density area and also whether such a lesion exists in the subdural-epiarachnoid space or in the subarachnoid space. A carotid angiographic evaluation of cortical vessels in the marginal avascular area was made and suggestive results were obtained. When there is acute subdural effusion or subdural hematoma, cortical arteries in the marginal avascular area will have a straightened and attenuated figure. But when such a pathologic state persists for a long period, it induces secondary cortical atrophy and the subarachnoid space becomes enlarged. The cortical artery appears as if it is flying in the enlarged subarachnoid space because it is detached from the gyrus and the sulcus following the cortical atrophy. This is why we named it the 'flying artery.' Angiographic findings allow more precise interpretation of the marginal low density area in the CT scan.