Arachnoid Webs Research Articles

Surgical Management of Thoracic Dorsal Arachnoid Webs: A Ten-Year Single-Institution Experience

ObjectiveThoracic dorsal arachnoid webs are intradural membranes that may cause obstruction of CSF flow and spinal cord compression. While well-recognized, they are rare and there is a paucity of long-term data on their natural history and prognosis. We reviewed radiographic features, surgical indications, and pathologic specimens of patients diagnosed with focal thoracic dorsal arachnoid webs. MethodsA radiology database and surgical case logs were queried for thoracic arachnoid webs at a single hospital system for a ten-year period. A retrospective chart review was performed on identified cases. ResultsWe identified 127 patients with dorsal thoracic arachnoid webs. Arachnoid webs were radiographically classified into three morphologic types: Type 1 (54%) causing spinal cord deformity only, Type 2 (32%) producing cord deformity with myelomalacia, and Type 3 (14%) with cord deformity, myelomalacia, and syringomyelia. These arachnoid webs were commonly centered at the upper thoracic T4 segmental level. Forty-one cases (32%) required surgery, generally for thoracic myelopathy with gait instability (46%) and lower extremity numbness and pain (39%). In patients who underwent surgery, 79% experienced symptomatic improvement and 21% remained stable, after an average of 21 months follow-up evaluation. Surgical pathology revealed fibrous connective tissue (100%) with calcifications (26%) or inflammation (7%). ConclusionsThe majority in a large series of patients with dorsal arachnoid webs did not undergo surgical intervention, but those with myelomalacia and syrinx experienced radiographic and clinical deterioration without surgery. Surgery to treat symptomatic arachnoid webs results in significant clinical improvement with low surgical morbidity.

Resection of an incidentally discovered spinal arachnoid web: illustrative case.

Spinal arachnoid webs (SAWs) are rare pathologies of the spinal meninges often associated with syringomyelia and the radiographic "scalpel sign." Patients can experience pain, numbness, gait disturbances, or no symptoms at all. They are typically diagnosed via magnetic resonance imaging and treated with laminectomy and excision. A 61-year-old male presented after a mechanical fall and had an incidentally discovered SAW on imaging. He was initially asymptomatic and was therefore conservatively managed. Several years later, however, the patient experienced new-onset back pain, paresthesia, and balance problems, with interval imaging demonstrating worsening of the edema surrounding his SAW. The patient subsequently underwent resection of the SAW, which led to significant resolution of his symptoms. An SAW can be asymptomatic or can manifest with a wide variety of symptoms. When this condition is incidentally discovered in asymptomatic patients, neurosurgeons should guide these patients to follow-up urgently if they develop any neurological symptoms. At that time, further imaging can be performed to determine if surgical treatment is indicated. Although SAW is rare, clinicians should be aware of the signs and symptoms, because prompt surgical intervention can significantly improve neurological symptoms.

Reappraisal of intradural findings in Chiari malformation type I.

Management of Chiari malformation type I (CM-I) requires the functional restoration of an obstructed cisterna magna. In posterior fossa decompression with duraplasty (PFDD), various intradural pathologies are suggested to alter CSF flow at the craniocervical junction and require surgical correction. However, reports of the spectrum of intraoperative intradural findings and their nuances are scarce, especially those characterizing rarer findings pertaining to the vascular structures and vascular compression. The authors conducted a retrospective cohort analysis of adults and children who underwent first-time PFDD for CM-I (2011-2021), with and without syringomyelia. The surgical reports and intraoperative videos were reviewed, and the frequency and nature of the intradural observations in regard to the tonsils, arachnoid, and vasculature were analyzed along with the clinical findings and surgical outcomes. All 180 patients (age range 1-72 years; median [interquartile range] 24 (14-38) years; 37% of patients were children < 21 years of age) exhibited multiple intradural findings, with a median of 7 distinct concurrent observations in each patient. Novel findings not previously reported included posterior inferior communicating artery (PICA) branches compressing the neural elements at the cervicomedullary junction (26.7%). Other common findings included arachnoid adhesions (92.8%), thickening (90.6%), webs at the obex (52.2%), tonsillar gliosis (57.2%), tonsillar hypertrophy (18.3%), adhesions obstructing the foramen of Magendie (FoM) (62.2%), PICA obstruction of the FoM (17.2%), and dural scarring (87.8%). Tonsillar gliosis and intertonsillar adhesions obstructing the FoM were more common in children than adults. Tonsillar gliosis and arachnoid webs were more common among syringomyelia patients. After multivariable adjustment, none of the observed findings were independently associated with syringomyelia, preoperative symptoms, or postoperative improvement. The vast majority of patients improved postoperatively. The complication rate was low: 1.2% of patients required revision PFDD at > 3 years postoperatively, 3.6% experienced other operative complications, and 0% had CSF leaks. The diversity of intradural findings and observations revealed in this study suggests that obstructive and compressive structural anomalies may be more common than previously reported among CM-I patients, both those patients with and those without syringomyelia and especially those with obstructive and compressive PICA branches. Although the authors cannot conclude that all these findings are necessarily pathological, further study may determine how they contribute to CM-I pathology and symptomatology in the setting of a compromised cisterna magna.

Clinical Characteristics, Outcomes, and Pathology Analysis in Patients With Dorsal Arachnoid Web.

Dorsal arachnoid webs (DAWs) are rare pathological abnormalities of the arachnoid layer of the spinal cord that can result in pain and myelopathy. To present clinical, imaging, and pathological characteristics of patients diagnosed with DAW, case illustrations, and a review of the literature. Seventeen cases of DAW between 2015 and 2019 at a tertiary medical center were retrospectively identified through a case log search. Patient characteristics, preoperative imaging, operative notes, and pathology reports were collected. Our main outcome assessed was postoperative resolution of symptoms. Odds ratios were used to determine associations between preoperative signs and symptoms with postoperative symptom resolution. The mean age of the cohort was 50.5 years (IQR = 16) and presented primarily with back pain (64.7%). On imaging, all patients were found to have the "scalpel sign," and nearly half had a syrinx present (41.2%). All DAWs were located in the thoracic spine, with the most common location being the midthoracic (70.6%). The mean follow-up length for all patients was 4.3 months. There were no preoperative symptoms significantly associated with postoperative symptom resolution; however, a trend was noted with the presence of a preoperative syrinx. Pathology samples consistently demonstrated fibroconnective or collagenous tissue with no evidence of inflammation or neoplasm. DAW is a rare pathology that can result in myelopathy or inappropriate interventions if misdiagnosed. Surgical intervention using laminectomy with intradural exploration should be considered in symptomatic patients with DAW because it is curative with a strong chance of preoperative symptom resolution with relatively low complication rates.

Spinal Arachnoid Webs: Presentation, Natural History, and Outcomes in 38 Patients.

Spinal arachnoid webs are rarely described bands of thickened arachnoid tissue in the dorsal thoracic spine. Much is unknown regarding their origins, risk factors, natural history, and outcomes. To present the single largest case series, detailing presenting symptoms and outcomes amongst operative and nonoperative patients, to better understand the role of intervention. This retrospective chart review identified 38 patients with arachnoid webs. Patient demographics, radiologic signs, symptoms, and surgical history data were extracted from the electronic medical record. Symptoms were divided by location and character. 28 patients were successfully contacted for follow up outcome surveys. 26 patients (68%) underwent surgical intervention, 12 (32%) were managed non-operatively. 15 (39%) patients had undergone a previous unsuccessful surgery at a different site for their symptoms prior to arachnoid web diagnosis. Commonly presenting symptoms included myelopathy (68%), focal thoracic back pain (68%), lower extremity weakness (45%), numbness and sensory changes (58%), and lower extremity radicular pain (42%), upper extremity weakness (24%), and radicular pain (37%). Focal thoracic pain was associated with thoracic level (P <.02). Myelopathic symptoms were less common in postoperative patients. Postoperative patients described significantly more upper extremity (P <.01) and thoracic (P <.01) numbness and paresthesias. Surveyed nonoperative patients universally described their symptoms as either stable or worsening. Spinal arachnoid webs present with thoracic myelopathy and back pain but can also present with upper extremity symptoms. Surgical intervention stabilizes or improves symptoms and is well received. Nonoperative patients do not spontaneously improve.

Scalpel Sign in Spine Pathology: Presentation in 3 Different Rare Diagnoses

The scalpel sign is a radiological finding observed on sagittal magnetic resonance imaging and computed tomography myelography corresponding to an indentation in the dorsal aspect of the spinal cord resembling a surgical scalpel blade. It is said to be a pathognomonic imaging discovery linked to dorsal arachnoid webs. However, other spine-related conditions may mimic dorsal arachnoid webs on magnetic resonance imaging, such as spinal arachnoid cysts or ventral spinal cord herniation, leading to misdiagnosis. A retrospective review was performed of cases involving 3 different diagnoses at our institution in the last 5 years that shared in common the characteristic focal dorsal indentation of the spinal cord. Of 7 cases identified, all but 1 were treated and confirmed intraoperatively. All lesions were located at the dorsal spinal cord. Magnetic resonance imaging was the study of choice for evaluation. Clinical manifestations included back pain and lower extremity numbness and weakness together with compressive myelopathy signs and urinary symptoms. Mean follow-up was 16.8 months with satisfactory postoperative results. Isolated radiological presentation of the scalpel sign is not sufficient to distinguish between dorsal arachnoid webs, arachnoid cysts, and ventral herniation of the spine. However, awareness of its importance is relevant for accurate curative surgical planning.

Neuroimaging of Spinal Cord and Cauda Equina Disorders.

This article reviews the neuroimaging of disorders of the spinal cord and cauda equina, with a focus on MRI. An anatomic approach is used; diseases of the extradural, intradural-extramedullary, and intramedullary (parenchymal) compartments are considered, and both neoplastic and non-neoplastic conditions are covered. Differentiating imaging features are highlighted. Although T2-hyperintense signal abnormality of the spinal cord can have myriad etiologies, neuroimaging can provide specific diagnoses or considerably narrow the differential diagnosis in many cases. Intradural-extramedullary lesions compressing the spinal cord have a limited differential diagnosis and are usually benign; meningiomas and schwannomas are most common. Extradural lesions can often be specifically diagnosed. Disk herniations are the most commonly encountered mass of the epidural space. Cervical spondylotic myelopathy can cause a characteristic pattern of enhancement, which may be mistaken for an intrinsic myelopathy. A do-not-miss diagnosis of the extradural compartment is idiopathic spinal cord herniation, the appearance of which can overlap with arachnoid cysts and webs. Regarding intrinsic causes of myelopathy, the lesions of multiple sclerosis are characteristically short segment but can be confluent when multiple. Postcontrast MRI can be particularly helpful, including when attempting to differentiate the long-segment myelopathy of neurosarcoidosis and aquaporin-4 (AQP4)-IgG-seropositive neuromyelitis optica spectrum disorder (NMOSD) and when characterizing spinal cord tumors such as primary neoplasms and metastases. Spinal dural arteriovenous fistula is another do-not-miss diagnosis, with characteristic MRI features both precontrast and postcontrast. Tract-specific white matter involvement can be a clue for diseases such as subacute combined degeneration, paraneoplastic myelopathy, and radiation myelitis, whereas gray matter-specific involvement can suggest conditions such as cord infarct, viral myelitis, or myelin oligodendrocyte glycoprotein (MOG)-IgG associated disorder. Knowledge of the neuroimaging findings of the many causes of spinal cord and cauda equina dysfunction is critical for both neurologists and neuroradiologists. A structured approach to lesion compartmental location and imaging feature characterization is recommended.

Repair of Thoracic Spinal Cord Herniation: 2-Dimensional Operative Video.

Spinal cord herniation is an uncommon surgically treatable cause of thoracic myelopathy and progressive paraplegia. The thoracic spinal cord focally protrudes through a defect in the dura, resulting in progressive weakness, numbness, and spasticity affecting the lower extremities, in addition to possible urinary symptoms. In this video, we present the case of a 69-yr-old female who presented with 3 yr of progressive thoracic myelopathy due to a thoracic spinal cord herniation at T4-T5. We demonstrate the surgical steps to lyse arachnoid webs, mobilize the spinal cord, reduce the spinal cord herniation, and repair the dural defect. Appropriate patient consent was obtained.

Spinal arachnoid web-a review article.

The spinal arachnoid web is an abnormal formation of an arachnoid membrane in the subarachnoid space. It is a rare entity with some degree of uncertainty surrounding its etiology. It can result in a displacement of the spinal cord causing pain and neurological symptoms as well as blockage of cerebrospinal fluid (CSF) flow and subsequent syringomyelia. The syrinx resulting from the altered CSF flow dynamics has been described to assume variable positions relative to the web itself. The "scalpel sign" is regarded as a pathognomonic feature of a spinal arachnoid web. The arachnoid web, however, is relatively thin and may be elusive of routine radiological investigations. As such, a myriad of preoperative and intraoperative investigations have been postulated to improve the sensitivity of detecting this abnormality. Management of spinal arachnoid webs ranges from conservative management to surgical excision where in the latter, the extent of excision remains the subject of debate. The authors herein present a review of the available information on this rare topic.

Letter to the Editor. Radiographic differentiation of idiopathic spinal cord herniation versus dorsal arachnoid webs.

Letter to the Editor. Radiographic differentiation of idiopathic spinal cord herniation versus dorsal arachnoid webs.

Microscope and Fiberscope-assisted Subarachnoid-Subarachnoid (S-S) Bypass: A Novel Surgical Technique to Reestablish Cerebrospinal Fluid Flow in Treating Dorsal Spinal Arachnoid Webs, Diagnosed by Cine-MRI.

A "dorsal spinal arachnoid web" is the thickened arachnoid band on the surface of the spinal cord which disturbs the cerebrospinal fluid (CSF) flow, known as a rare cause of thoracic myelopathy. The ideal treatment is controversial because of the risk of readhesion after simple resection of the web. A subarachnoid-subarachnoid bypass is a method to reestablish CSF flow through a silicon tube between the cranial and caudal subarachnoid space. This method is reported to be useful for traumatic syringomyelia, adhesive arachnoiditis, etc. We applied this technique for arachnoid webs with the assistance of a microscope and fiberscope. After a dura incision, the thickened arachnoid web can be seen fluttering within the CSF flow inside the arachnoid space, which partitions the subarachnoid space into cranial and caudal parts. After opening the subarachnoid space and resection of the web under a microscope, the fiberscope is inserted toward the cranial and caudal directions to check for the presence of another arachnoid web. If another web is found, it is penetrated using a guiding wire. Then, a silicone tube is inserted into the cranial and caudal normal subarachnoid space. In this paper, we would like to introduce this technique.

Spinal Intradural Arachnoid Webs Causing Spinal Cord Compression with Inconclusive Preoperative Imaging: A Report of 3 Cases and a Review of the Literature

Spinal arachnoid webs are a rare variant of spinal arachnoid cysts where 1 or multiple focal membranes of arachnoid tissue obstruct the subarachnoid space. Only 11 prior cases of arachnoid webs have been reported in the literature. We present a series of 3 consecutive cases of arachnoid webs from our institution and review the literature on this rare condition to provide recommendations for its management. Retrospective chart review was performed for 3 consecutive cases of intradural arachnoid webs causing spinal cord compression at our institution, with inconclusive preoperative imaging, treatment with surgical decompression, and resection. There were no external sources of funding. Our cases occurred dorsally in the thoracic spine and were associated with syringomyelia. Preoperative magnetic resonance imaging, computed tomography myelography, and cine magnetic resonance imaging were inconclusive, and the definitive diagnosis was made with intraoperative ultrasound. Patients underwent laminectomies and resection of arachnoid webs. Unique from prior reports of arachnoid webs, the webs in the present cases were composed of multiple septated longitudinal membranes rather than a transverse band. All patients had improvement of presenting symptoms postoperatively. Intradural arachnoid webs causing spinal cord compression are rare. Preoperative imaging may be inconclusive. Because of the septated longitudinal nature of the visualized membranes, we propose a 1-way valve mechanism of cerebrospinal fluid obstruction causing gradual cord compression and resultant syringomyelia.

Response to “syringomyelia secondary to 'occult' dorsal arachnoid webs: Report of two cases with review of literature” by Sayal et al.

Response to “syringomyelia secondary to 'occult' dorsal arachnoid webs: Report of two cases with review of literature” by Sayal et al.

Identification of arachnoid web with a relatively novel magnetic resonance imaging technique

Arachnoid webs are described as intradural extramedullary transverse bands of arachnoid tissue that extend to the dorsal surface of the spinal cord, causing mass effect and dorsal indentation, and they are often associated with syringomyelia [ [1] Reardon M.A. Raghavan P. Carpenter-Bailey K. Mukherjee S. Smith J.S. Matsumoto J.A. et al. Dorsal thoracic arachnoid web and the “scalpel sign”: a distinct clinical-radiologic entity. Am J Neuroradiol. 2013; 34: 1104-1110 Crossref PubMed Scopus (66) Google Scholar ]. Although the precise mechanism of syrinx formation is unknown, dissection of the arachnoid web shrinks the syrinx and improves the symptoms [ 2 Chang H.S. Nagai A. Oya S. Matsui T. Dorsal spinal arachnoid web diagnosed with the quantitative measurement of cerebrospinal fluid flow on magnetic resonance imaging. J Neurosurg Spine. 2014; 20: 227-233 Crossref PubMed Scopus (32) Google Scholar , 3 Sridharan A. Heilman C.B. Transverse dorsal arachnoid web and syringomyelia. Neurosurgery. 2009; 65: E216-E217 Crossref PubMed Scopus (6) Google Scholar ]. Arachnoid webs are not easily visualized with conventional magnetic resonance imaging (MRI) or computed tomography (CT) myelography because of their comparatively thin width relative to other structures [ [2] Chang H.S. Nagai A. Oya S. Matsui T. Dorsal spinal arachnoid web diagnosed with the quantitative measurement of cerebrospinal fluid flow on magnetic resonance imaging. J Neurosurg Spine. 2014; 20: 227-233 Crossref PubMed Scopus (32) Google Scholar ]. Other institutions have described the use of cardiac-gated phase-contrast cine-mode MRI in multiple axial planes to better identify these entities radiographically [ [2] Chang H.S. Nagai A. Oya S. Matsui T. Dorsal spinal arachnoid web diagnosed with the quantitative measurement of cerebrospinal fluid flow on magnetic resonance imaging. J Neurosurg Spine. 2014; 20: 227-233 Crossref PubMed Scopus (32) Google Scholar ]. We report the use of a heavily T2-weighted constructive interference in steady state (CISS) sequence to identify these lesions preoperatively.

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.

Idiopathic syringomyelia: retrospective case series, comprehensive review, and update on management

A syrinx is a fluid-filled cavity within the spinal cord that can be an incidental finding or it can be accompanied by symptoms of pain and temperature insensitivity. Although it is most commonly associated with Chiari malformation Type I, the advancement of imaging techniques has resulted in more incidental idiopathic syringes that are not associated with Chiari, tumor, trauma, or postinfectious causes. The authors present a comprehensive review and management strategies for the idiopathic variant of syringomyelia. The authors retrospectively identified 8 idiopathic cases of syringomyelia at their institution during the last 6 years. A PubMed/Medline literature review yielded an additional 38 articles. Two of the authors' patients underwent surgical treatment that included a combination of laminectomy, lysis of adhesions, duraplasty, and syrinx fenestration. The remaining 6 patients were treated conservatively and had neurologically stable outcomes. Review of the literature suggests that an etiology-driven approach is essential in the diagnosis and management of syringomyelia, although conservative management suffices for most cases. In particular, it is important to look at disturbances in CSF flow, as well as structural abnormalities including arachnoid webs, cysts, scars, and a diminutive posterior fossa. The precise etiology for idiopathic syringomyelia (IS) is still unclear, although conceptual advances have been made toward the overall understanding of the pathophysiology of IS. Various theories include the cerebellar piston theory, intramedullary pulse pressure theory, and increased spinal subarachnoid pressure. For most patients with IS, conservative management works well. Continued progression of symptoms, however, could be approached using decompressive strategies such as laminectomy, lysis of adhesions, and craniocervical decompression, depending on the level of pathology. Management for patients with progressive neurological dysfunction and the lack of flow disturbance is unclear, although syringosubarachnoid shunting can be considered.

CARDIAC-GATED PHASE-CONTRAST MAGNETIC RESONANCE IMAGING OF CEREBROSPINAL FLUID FLOW IN THE DIAGNOSIS OF IDIOPATHIC SYRINGOMYELIA

Syringomyelia without an obvious cause, such as a Chiari malformation, a tumor, or a spinal injury, is rare and may be associated with an arachnoid web or cyst. In the literature, conventional myelography is the diagnostic method of choice. In this retrospective study, we evaluated the diagnostic value of magnetic resonance imaging (MRI) cerebrospinal fluid (CSF) flow studies as compared with conventional myelography in patients with syringomyelia. From early 2003 to late 2006, 320 patients with syringomyelia underwent cardiac-gated phase-contrast MRI of CSF flow in the brain and spine. We assessed the presence of CSF flow blockage as well as syrinx site, shape, and size. Additional myelography was performed in 8 patients. CSF flow blockage and progressive neurological symptoms or progression of syringomyelia were indications for surgery. Syringomyelia without an obvious cause was found in 125 patients. CSF flow blockage was detected in 33 patients. Seven of these patients underwent cyst wall resection and decompression of the subarachnoid space via a unilateral approach without laminectomy. Myelography revealed CSF flow blockage in only 2 of 8 cases. In the other 6 patients, MRI detected a blockage and surgery revealed arachnoid cysts or webs. Postoperative CSF flow studies revealed free CSF flow in all 10 surgically treated patients. In 6 of these patients, syrinx size was reduced after surgery. Myelography should not be the method of choice for the diagnosis of idiopathic syringomyelia. MRI CSF flow studies were found to be more reliable.

Three-dimensional constructive interference in steady-state magnetic resonance imaging in syringomyelia: advantages over conventional imaging

Neuroradiology has become indispensable in detecting the pathophysiology in syringomyelia. Constructive interference in steady-state (CISS) magnetic resonance (MR) imaging can provide superior contrast at the sub-arachnoid tissue borders. As this region is critical in preoperative evaluation, the authors hypothesized that CISS imaging would provide superior assessment of syrinx pathology and surgical planning. Based on records collected from a database of 130 patients with syringomyelia treated at the authors' institution, 59 patients were prospectively evaluated with complete neuroradiological examinations. In addition to routine acquisitions with FLAIR, T1- and T2-weighted, and contrast-enhanced MR imaging series, the authors obtained sagittal cardiac-gated sequences to visualize cerebrospinal fluid (CSF) pulsations and axial 3D CISS MR sequences to detect focal arachnoid webs. Statistical qualitative and quantitative evaluations of spinal cord/CSF contrast, spinal cord/CSF delineation, motion artifacts, and artifacts induced by pulsatile CSF flow were performed. The 3D CISS MR sequences demonstrated a contrast-to-noise ratio significantly better than any other routine imaging sequence (p < 0.001). Moreover, 3D CISS imaging can detect more subarachnoid webs and cavitations in the syrinx than T2-weighted MR imaging with less flow-void artifact. The limitation of 3D CISS imaging is a susceptibility to motion artifacts that can cause reduced spatial resolution. Lengthy acquisition times for axial segments can be reduced with multiplanar reconstruction of 3D CISS-generated sagittal images. Constructive interference in steady-state imaging is the MR sequence of choice in the preoperative evaluation of syringomyelia, allowing significantly higher detection rates of focal subarachnoid webs, whereas standard T2-weighted MR imaging shows turbulent CSF flow voids. Constructive interference in steady-state MR imaging enables the neurosurgeon to accurately identify cases requiring decompression for obstructed CSF. Motion artifacts can be eliminated with technical variations.

Idiopathic syringomyelia and the importance of occult arachnoid webs, pouches and cysts

Syringomyelia is the condition in which longitudinal cavities are found within the spinal cord. The use of drainage procedures has been widely practised with good short term results. However, the long-term results in some large series have been less favourable. There are many associated conditions and in most forms a blockage to the normal flow of CSF, either at the foramen magnum or in the spinal canal, can be identified. Most surgeons would now direct their efforts to the establishment of normal CSF flow rather than a shunting procedure. In a certain group of patients, even with the advent of sophisticated MRI, no associated abnormality or CSF block is easily identified. This type of syringomyelia is often termed idiopathic. We report 10 patients with symptomatic syringomyelia without readily recognized predisposing factors. In eight patients preoperative myelography revealed a block to the flow of contrast compatible with subarachnoid obstruction. Eight patients underwent laminectomy and division of the obstructing arachnoid webs. Five experienced good improvement and three only moderate improvement. Two of the patients underwent syrinx shunting procedures only, which resulted in a worsening of their symptoms. At operation one patient was found to have an arachnoid cyst. We believe that patients with idiopathic symptomatic syringomyelia may need myelography to identify such arachnoid abnormalities. Subsequent surgery should be directed at the establishment of normal CSF flow by laminectomy and excision of the offending lesion.