Ectopic arachnoid granulation involving a rare intracranial venous sinus variant.

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.

Arachnoid granulations: a rare cause of lytic occipital bone lesion.

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.

Management of infratentorial subdural hygroma complicating foramen magnum decompression: a report of three cases.

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.

[Arachnoid granulations of the posterior temporal bone wall: report of two cases]. / Granulations arachniïdiennes de la face postérieure du rocher : à propos de deux cas.

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.

Giant arachnoid granulation in a patient with benign intracranial hypertension (2009: 1b).

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.

Causes of arachnoid cyst development and expansion.

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.

MR of giant arachnoid granulation, a normal variant presenting as a mass within the dural venous sinus.

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.

Agenesis of arachnoid granulations and its relationship to communicating hydrocephalus.

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.

Arachnoid veils and the Chiari I malformation.

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.

Stereotactic catheter insertion: a new technique.

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.

CSF dynamics in hydrocephalus--with special attention to external hydrocephalus.

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.

Surgical treatment of a syringomyelia associated with an idiopathic arachnoid malformation disclosed by preoperative MRI.

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.

Congenital ocular motor apraxia. Case reports and literature review.

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.

[Arachnoid cysts: histologic, embryologic and physiopathologic review]. / Les kystes arachnoïdiens : mise au point histologique, embryologique et physio-pathologique.

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.

[Spontaneous rhinorrhea due to (congenital?) evagination of arachnoidea in the paranasal sinuses]. / Rhinorrhée spontanée parévagination (congénitale?) de l'arachnoïde dans les sinus para-nasaux

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.

[Arachnoid cysts (pathomorphological studies)]. / Arakhnoidal'nye kisty (patomorfologicheskie issledovaniia).

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.

Dorsal spinal arachnoid web diagnosed with the quantitative measurement of cerebrospinal fluid flow on magnetic resonance imaging.

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.

Dorsal thoracic arachnoid web and the "scalpel sign": a distinct clinical-radiologic entity.

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.

Intrasacral meningocele in the pediatric population.

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.