Scalpel Sign Research Articles

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.

Dorsal arachnoid web: the ‘scalpel’ sign—a case report and differential diagnosis

BackgroundArachnoid web of the spine is a not so common lesion of the spinal cord. It is a band-like arachnoid tissue in the intradural extramedullary compartment that extends to the surface of the spinal cord, with a tendency to occur in the upper dorsal spine causing focal dorsal indentation of the cord that has been coined the ‘scalpel sign’. Patients usually present with progressive weakening and numbing of bilateral lower limb.Case presentationA 58-year-old man presented with difficulty in walking and weakness of right leg for 1 year, aggravated over the previous 2 months. There was no history of trauma or fever. Magnetic resonance imaging (MRI) of the dorsal spine was done which revealed a small syrinx within the cord at D4 vertebral level on right side. There was sharp dorsal indentation of the spinal cord and widening of the arachnoid space below this level. This appearance was similar to a surgical scalpel. The anterior subarachnoid space was preserved. On post-contrast images, no parenchymal or meningeal enhancement was detected. The patient was taken up for surgery as the symptoms further progressed. Laminectomy was done from D3 to D7 under general anesthesia, with release of arachnoid web and adhesions. Histology of the resected specimen revealed epithelial cells and fibrous tissue. No inflammatory or neoplastic cells were observed.ConclusionsThoracic arachnoid web is a rare entity, which if not treated can have devastating effects on a patient’s neurological function. Careful evaluation of radiological findings is important to avoid delay in diagnosis. Surgery is the only curative treatment and is known to have a favorable outcome.

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.

Minimally Invasive Approach for Dorsal Arachnoid Web: 2-Dimensional Operative Video.

A 67-yr-old patient presented with severe paraparesis and lower limb spasticity. The spinal cord magnetic resonance imaging (MRI) revealed the "scalpel sign" 1,2 at the T7 level, suggesting a diagnosis of a dorsal arachnoid web. This video demonstrates a microsurgical technique for the excision of a dorsal arachnoid web with a minimally invasive approach. A paramedian skin incision, understanding the muscular aponeurosis, was performed from T7 to T8. Then, we inserted the tubular dilators until the lamina, to perform a muscle-sparing approach. An expandable tubular retractor of adequate length was passed over the widest dilator and docked into place along the subperiosteal plane. The T7 lamina was drilled, and the resection of the superior and inferior adjacent spine levels was completed with a rongeur. Additional contralateral bone resection was performed after tubular retractor tilt to the midline.3 After dura mater opening, it was carefully suspended and the dorsal arachnoid leaflet was cut to drain the dorsolateral and lateral spinal cisterns.4 The dorsal arachnoid web was, first, disconnected from its lateral anchorages. It was then gently removed with microsurgical forceps, to help its microdissection from the spinal cord surface. At this step, peculiar attention was paid to limit the traction or displacements of the spinal cord and surrounding vessels. Once the dorsal arachnoid web was removed, the quality of the spinal cord decompression was confirmed by its re-expansion. In conclusion, the minimally invasive approach is a safe and appropriate technique for dorsal arachnoid web excision.2,5,6-7 The patient gave her informed and signed consent for the writing and publication of this article. Image at 1:00 reused with permission from Castelnovo G et al, Spontaneous transdural spinal cord herniation, Neurology, 2014;82(14):1290.

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.

Spinal Arachnoid Web: A didactic report of two cases with clinical, radiological, surgical and pathological correlations

BackgroundArachnoid web (AW) is a rare but probably underestimated cause of spinal cord injury that is complex to diagnose due to subtle MRI findings and similarities to other better-known diseases such as arachnoid cyst (AC) or transdural spinal cord herniation (TSCH). Increased recognition of AW is mandatory since delay in diagnosis can lead to potentially serious neurological sequelae. Case presentationsWe report two additional cases of AW for didactic purposes, with special emphasis on the distinctive MRI and intraoperative findings. Both patients presented with progressively worsening neurological symptoms, including proprioceptive ataxia, motor weakness, numbness and neuropathic pain. The diagnosis of AW was suspected on the basis of specific MRI criteria, especially the so-called “scalpel sign”. Formal confirmation of the diagnosis was obtained in two patients that were managed surgically. Postoperative follow-up demonstrated significant functional recovery. DiscussionThere is a need for better recognition of AW by the medical community. Careful analysis of MRI semiology is crucial for the distinction between AW, AC and TSCH. Prompt and accurate diagnosis is mandatory to conserve functional prognosis, since appropriate surgical treatment with AW resection is curative, halting or even resolving the neurological symptoms.

Spinal arachnoid web—a distinct entity of focal arachnopathy with favorable long-term outcome after surgical resection: analysis of a multicenter patient population

BACKGROUND CONTEXTSpinal arachnoid web (SAW) is a rare condition characterized by focal thickening of the arachnoid membrane causing displacement and compression of the spinal cord with progressive symptoms and neurological deficits. Recent reports and clinical experience suggest that SAW is a distinct entity with specific radiological findings and treatment strategies distinguishable from other arachnopathies and potential differential diagnoses. PURPOSETo better define the diagnostic and clinical features, treatment options and outcomes of surgically treated SAW. STUDY DESIGNMulticentric retrospective cohort study. PATIENT SAMPLETwelve cases of SAW surgically treated at three different centers. OUTCOME MEASURESSelf-reported and neurological outcome measurements (pain, sensory-motor deficits, vegetative dysfunctions) were assessed at follow-up timepoints. METHODSRetrospective review of prospectively collected data on all patients surgically treated for SAW from three participating neurosurgical centers between 2014 and 2020. Clinicopathological data, including neurological presentation, radiological and histological findings and outcome data were analyzed. RESULTSTwelve radiologically and surgically confirmed cases of SAW were analyzed. Mean patient age was 54.7 [±12.7], 67% were male. All SAWs were located in the posterior thoracic dural sac. On magnetic resonance imaging (MRI), the “scalpel sign” - a characteristic focal dorsal indentation of the spinal cord resembling a scalpel blade - was identified in all patients. A focal intramedullary syrinx was present in 83%. Preoperative clinical symptoms included signs of myelopathy, pain, weakness and sensory loss, most commonly affecting the trunk/upper back or lower extremities. Laminectomy or laminoplasty with intradural excision of the SAW was the surgical treatment of choice in all cases. Intraoperative ultrasound was valuable to visualize the cerebrospinal fluid (CSF) flow obstruction, confirm the SAW location before dura incision and to control adequacy of resection. After surgery, sensory loss and weakness in particular showed significant improvement. CONCLUSIONSThe present study comprises the largest series of surgically treated SAW, underscoring the unique clinical, radiographic, histopathological, and surgical findings. We want to emphasize SAW being a distinct entity of spinal arachnopathy with a favorable long-term outcome if diagnosed correctly and treated surgically. Intraoperative ultrasound aids visualizing the SAW before dural incision, as well as verifying restored CSF flow after resection.

Multi-modality imaging evaluation of the dorsal arachnoid web.

Dorsal arachnoid web (DAW) is a rare intradural abnormality which is associated with progressive myelopathy. Our objective was to review multi-modality imaging techniques demonstrating the scalpel sign appearance in evaluation of DAW. We retrospectively reviewed various imaging modalities of patients found to have DAW at our institution during January 2015 to February 2020. Five patients underwent surgical decompression with pathological correlation. The remaining patients were presumptively diagnosed based on the characteristic finding of scalpel sign. Clinical data were evaluated and correlated to imaging findings. All imaging modalities demonstrated the characteristic scalpel sign. Sixteen patients (10 females, and six males) with multi-imaging modalities were evaluated. Their mean age was 52 year (range 23-74 years). Fifteen patients underwent conventional spine MRI. Further high-resolution MR imaging techniques, e.g. 3D T2 myelographic sequence, were utilized with two patients. MRI spine CSF flow study was performed to evaluate the flow dynamic across the arachnoid web in one patient. Eight patients were evaluated with CT myelogram. Syrinx formation was discovered in seven (44%) patients; five (71%) of them underwent surgical resection and decompression. Two patients underwent successful catheter-directed fenestration of the web with clinical improvement. We found a statically significant positive correlation between the degree of cord displacement and compression with syrinx formation (r = 0.55 and 0.65 with p-value of 0.03 and 0.009, respectively). DAW has characteristic scalpel sign independent of imaging modality. Multi-modality imaging evaluation of DAW is helpful for evaluation and surgical planning.

Posterior spinal cord indentation: imaging findings and clinical outcome

To identify the imaging findings associated with worse clinical outcome in posterior spinal cord indentation. A retrospective search for cases of dorsal cord indentation on magnetic resonance imaging (MRI) from April 2009 to March 2016 was undertaken. Imaging follow-up and clinical data were recorded. Two neuroradiologists blinded to the clinical data assessed the imaging findings. Differences and association of imaging and clinical findings were assessed via t-test and Fisher's exact and chi-squared tests for continuous and categorical data. Inter-rater agreement was calculated. Seventy-three patients were included, 65 were clinically stable, or the finding was incidental and eight had clinical worsening or required surgery. There was a significant difference in the percentage of cord diameter decrease between the two clinical groups (p=0.013, reader 1; p=0.027 reader 2). The clinical course was significantly associated with subjective cord indentation depth assessment (p=0.03 reader 1) and presence of syrinx (p=0.017 reader 2) on original MRI and worsening on imaging follow-up (p=0.03). The interrater agreement was moderate for syrinx identification (k=0.58). There was only fair agreement for the scalpel sign classification and in the final diagnosis (k=0.35 and 0.28). The degree of cord indentation, the presence of syrinx, and worsening of imaging findings on follow-up are associated with worse clinical course and can be useful in guiding management and directing subspecialty referrals.

Imaging Findings in Dorsal Thoracic Arachnoid Web and the Differential Diagnosis of “Scalpel Sign”

A dorsal thoracic arachnoid web represents an intradural extramedullary transverse band of arachnoid tissue that causes mass effect and dorsal cord indentation, and can or cannot be associated with spinal cord altered signal. On sagittal MR imaging, this focal dorsal indentation of the thoracic spinal cord resembles a scalpel with its blade pointing posteriorly (called a “scalpel sign”). Although very suggestive of dorsal thoracic arachnoid web, this sign is not specific and should be differentiated from other ventral cord displacement causes (eg, idiopathic spinal cord herniation and spinal arachnoid cyst). In idiopathic spinal cord herniation, cord tissue protrudes through a ventral dural defect, and the focal deformity can be seen along the ventral aspect of the cord on spinal axial MR imaging and with a characteristic “C sign” on sagittal MR imaging; in spinal arachnoid cysts, the marginated walls and the presence of smooth, wide scalloping of the cord surface can be identified. Recognition of these imaging findings, especially the scalpel sign, can help radiologists and clinicians make a correct diagnosis of ventral cord displacement causes and allow subsequent prompt treatment for the patient.

Intradural Extramedullary Surgical Lysis of an Arachnoid Web of the Spine: 2-Dimensional Operative Video.

Arachnoid web of the spine (AWS) is a rare and subtle lesion that can have severe neurological consequences. Patients typically present with progressive myelopathic symptoms and have no more than a slight indentation of spinal cord on imaging, commonly referred to as the "scalpel sign." A unique feature associated with this lesion is the extent of (and sometimes the rapidity of) the recovery that occurs following treatment. In this operative video, we highlight the treatment of a 32-yr-old male with a history of lumbar spondylosis, who, over a 2 wk period, developed progressive spasticity and weakness of the entire left lower extremity and left foot numbness. Magnetic resonance imaging revealed a T4-T5 "scalpel sign" and spinal cord compression on computed topography myelogram, which was subsequently taken to the operating theater. The major steps in this video include the following: A) a summary of the patient's presentation and preoperative imaging, B) the technical steps in the surgical lysis of the AWS, and C) his postoperative course. The patient tolerated the procedure well, demonstrating a rapid improvement in symptoms postoperative day 1. At the time of most recent follow-up (4 mo), the patient remains neurologically intact with a full return to his neurologic baseline. Surgical lysis of AWS demonstrated to be a curative procedure with rapid neurological recovery, showing no signs of recurrence or regression. Consent was given by the patient for the use of deidentified images and the intraoperative video for educational purposes at the time consent was obtained for the surgical procedure, in accordance with our institution's policy.

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.

Dorsal Arachnoid Web and Scalpel Sign: A Diagnostic Imaging Entity.

A case of 60-year-old woman with idiopathic syringomyelia and progressive myelopathy by dorsal arachnoid web is discussed. One focal indentation along the dorsal surface of the spinal cord at the T3 vertebral body level revealed the scalpel sign, a radiologic entity diagnostic of a dorsal thoracic arachnoid web. T2-T3 laminectomy for the resection of dorsal arachnoid band was performed. Careful sectioning of the web resulted in visual apparent relief of the compression and good functional recovery. In patients with presumed idiopathic syringomyelia, imaging studies should be closely inspected for the presence of transverse arachnoid web. This extramedullary transverse band of arachnoid tissue extends to dorsal surface of the spinal cord, resulting in mass effect and dorsal indentation, known as scalpel sign because of its apparent resemblance to a scalpel on sagittal imaging. Early diagnosis with early intervention may benefit greatly patients. Surgical resection of transverse arachnoid web is a minimally invasive procedure with low morbidity, and can result in resolution of syringomyelia and improvement in neurological function.

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.

61.: Dorsal thoracic arachnoid web and the scalpel sign

We draw attention to a recently described radiological sign which will aid early identification of this rare type of intradural extramedullary thoracic spine disorder. We report three patients from a tertiary hospital in New Zealand with myelopathy due to dorsal thoracic arachnoid web, the unique radiological features, intraoperative findings and histology. The radiological “scalpel sign” was demonstrated in all three patients (two men and one woman, aged 40–50 years) with spastic paraparesis, thoracic spinal sensory level and sphincter disturbances. All patients underwent surgery with radiological improvement and subsequent resolution of symptoms. Dorsal thoracic arachnoid web is a rare but potentially curative form of thoracic myelopathy, which if identified and corrected early appears to result in good functional outcome.

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.