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Non-Tumoral Dorsal Thoracic Cord Deformity: Differential Diagnosis, Pre-Operative Imaging Evaluation and Intraoperative Correlation Daniel Noujaim, MD Dann Martin, MD Department of Radiology Lahey Hospital and Medical Center Burlington, MA

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Purpose To describe non-tumoral dorsal thoracic cord deformity To discuss pertinent differential considerations To demonstrate the benefit of pre-operative imaging To correlate imaging diagnosis with intra- operative findings

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Approach Case examples will be used to highlight Imaging findings Differential diagnosis Advanced imaging techniques Post surgical findings

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Background Deformities of the dorsal thoracic cord are occasionally identified on MR imaging in patients presenting with myelopathy Clinically described symptoms have included: Lower extremity paresthesia and weakness Gait disturbance Upper extremity paresthesia and weakness Neck and upper back pain Or combination of above symptoms Clinical course is usually progressive and long standing

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Differential Diagnosis Intradural Arachnoid Cyst (Nabors type III arachnoid cyst) Ventral Thoracic Cord Herniation Dorsal Thoracic Arachnoid Web Clinical presentation and routine MR imaging appearance for these entities overlap

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Goal of Presentation To provide clues on routine imaging that can guide differential diagnosis and further pre- operative imaging characterization

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CASE EXAMPLES

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Case 1 History: 46 y.o. male with progressive bilateral lower extremity paresthesia for several years. Also, erectile dysfunction and occasional difficulty emptying bladder.

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Case 1 History: 46 y.o. male with progressive bilateral lower extremity paresthesia for several years. Also, erectile dysfunction and occasional difficulty emptying bladder.

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Case 1 Findings: Sagittal Ventral displacement of thoracic cord over multiple vertebral levels Absent CSF pulsation flow artifact at levels of cord displacement Axial Flattening of dorsal thoracic cord without cord signal abnormality

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Arachnoid Cyst Split in the arachnoid layers that fills with CSF and forms a cyst Spinal arachnoid cysts are most commonly thoracic and dorsal to cord

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Arachnoid Cyst Post Operative Imaging: 1.Resolved cord deformity 2.Subtle residual thoracic cord volume loss from chronic compressive myelomalacia Symptoms: Improved, but not resolved

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MIMICS of Arachnoid Cyst Neuroenteric Cyst Epidermoid Cyst Arachnoiditis Neurocysticercosis

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MIMICS of Arachnoid Cyst Neuroenteric Cyst Type of foregut duplication cyst, which can be intracranial or intraspinal Spinal lesions are most commonly thoracic and associated with vertebral (+/- spinal cord) anomalies, as in this case (T2-T3 fusion), from incomplete regression of neuroenteric canal Note: Absent pulsation flow artifact within the cyst on T2 Internal T1 signal and vertebral anomaly favor neuroenteric cyst

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MIMICS of Arachnoid Cyst Arachnoiditis Inflammatory disease of the arachnoid caused by: Infection Surgery Unintended intrathecal steroid injection and Subarachnoid Hemorrhage as in this case of remote PICA aneurysm rupture treated with coiling Note: Persistent CSF pulsation artifact and multifocality of disease

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Case 2 History: 59 y.o. Female with 8 month history of right lower extremity weakness. Some urinary incontinence for 6 weeks. Six recent falls.

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Case 2 History: 59 y.o. Female with 8 month history of right lower extremity weakness. Some urinary incontinence for 6 weeks. Six recent falls.

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Case 2 History: 59 y.o. Female with 8 month history of right lower extremity weakness. Some urinary incontinence for 6 weeks. Six recent falls.

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Case 2 Findings: 1.Preserved dorsal CSF pulsation artifact 2.Kinking of thoracic cord 3.Extradural fluid collection suggestive of CSF leak from dural defect

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Ventral Thoracic Cord Herniation Herniation of thoracic cord through a dural defect Cause usually idiopathic, however antecedent trauma, hyperflexion and disc herniation have been proposed Herniation typically occurs at apex of thoracic curvature (T2-T6), where cord opposes ventral theca Typical presentation: Long-standing myelopathy or Brown-Sequard Syndrome (ispsilateral spastic paralysis with contralateral pain and temperature loss)

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Case 3 History: 52 y.o. Male progressive bilateral lower extremity weakness and numbness over 12 years.

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Case 3 History: 52 y.o. Male progressive bilateral lower extremity weakness and numbness over 12 years.

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Case 3 Findings: 1.Focal ventral flattening of thoracic cord 2.Adjacent syrinx 3.Preserved dorsal CSF pulsation artifact with thin dorsal arachnoid membrane (red arrow)

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Case 3 Myelogram Findings: Early Phase: Thin septation Differential contrast desity across septation (red arrow) Late Phase (2 hour delay) : Septation less apparent Homogenous contrast density across septation Fluoroscopy (at time of contrast instillation) Delay in contrast ascent Thin column of contrast passing under web, adjacent to cord (red arrow)

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Case 3 Post Operative Imaging: 1.Resolved cord deformity 2.Residual myelomalacia Clinical Symptoms: Improved, but not resolved

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Dorsal Thoracic Arachnoid Web Intradural extramedullary band of arachnoid tissue that can extend to the pial surface of the thoracic cord, causing focal dorsal cord deformity Occur in the upper thoracic spine and produce a characteristic cord deformity on MRI recently termed the scalpel sign(Reardon, et al.) Typical presentation: Myelopathy

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Dorsal Thoracic Arachnoid Web Companion Case: 56 y.o. Male with long standing and progressive bilateral lower extremity paresthesia and weakness Findings: Subtle dorsal thoracic cord defomity (subtle Scalpel Sign) Preserved dorsal CSF pulsation artifact Myelogram confirms absence of an arachnoid cyst

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Dorsal Thoracic Arachnoid Web Companion Case: 56 y.o. Male with long standing and progressive bilateral lower extremity paresthesia and weakness Post Operative Imaging: Resolved dorsal cord deformity Clinical Symptoms: Improved lower extremity strength, with mild residual lower extremity paresthesia

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Intraoperative Correlation Before Web ResectionAfter Web Resection

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Imaging Assessment Algorithm LocationMR appearanceCSF pulsation artifact MyelogramDDX Arachnoid Cyst Any Location Dorsal to Cord Segmental Ventral Displacement of the Cord Absent Inside Cyst Absent or Partial Filling of Cyst Neuro- enteric Cyst Epidermoid Arachnoiditis Cord Herniation Apex of Thoracic Kyphosis Focal Ventral kinking of the Cord Preserved Look for: Epidural CSF Leak No Filling Defect (Potentially Dural Leak) Thoracic Web, if No Clear Cord Herniation or CSF Leak Thoracic Web Upper Thoracic Spine Focal Ventral Displacement of the Cord with or without Syrinx Preserved Look for: Thin Membrane at Deformity No filling defect (Potentially Contrast Delay at Web) Subtle Cord Herniation, without CSF Leak

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Advanced Pre-Surgical Imaging CT Myelogram Early phase imaging with consideration for delayed imaging if filling defect or delay identified. High Resolution (steady-state) MRI [FISP (Siemens), CISS-FIESTA (GE), FFE (Philips)] May show cyst wall (right) or web membranes Phase Flow Imaging False Negatives in cases of arachnoid web, because one flow direction usually persists FIESTA

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Summary Careful evaluation for dorsal thoracic cord deformities is recommended in patients presenting with suspected myelopathy (regardless of cord signal) Complete preoperative imaging might include high resolution MR sequences and/or CT myelography Preoperative imaging might better direct pre- surgical assesment and help avoid unnecessary procedures, such as syrinx shunting or cord biopsy, potentially leaving primary causes untreated

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References SE Noujaim, KL Moreng, and DL Noujaim. Cystic Lesions in Spinal Imaging: A Pictorial Review and Classification. Neurographics 2013; 3:14-27 TA Mattei. Imaging is not everything: thoracic intradural arachnoid cyst with severe spinal cord compression in an asymptomatic patient. The Spine Journal 2012; 12:1077 S Ghostine, EM Baron, B Perri, et al. Thoracic cord herniation through a dural defect: description of a case and review of the literature. Surgical Neurology 2009; 71:362367 MA Reardon, P Raghavan, K Carpenter-Bailey, et al. Dorsal Thoracic Arachnoid Web and the Scalpel Sign: A Distinct Clinical-Radiologic Entity. AJNR 2013; 34(5):1104-10 HS Chang, A Nagai, S Oya, and T Matsui. Dorsal spinal arachnoid web diagnosed with the quantitative measurement of cerebrospinal fluid flow on magnetic resonance imaging: Report of 2 cases. J Neurosurg Spine 2014; 20:227233 SS Grewal, SM Pirris, PG Vibhute, V Gupta. Identification of arachnoid web with a relatively novel magnetic resonance imaging technique. The Spine Journal 2015; 15:554555