Unmasking the role of a thoracic arachnoid web and watershed ischemia in rapidly progressing paraplegia: illustrative case.

BACKGROUND

Spinal arachnoid webs (SAWs) are an uncommon cause of spinal cord compression, typically presenting with an insidious onset of symptoms. Their role in acute neurological deterioration is not well established, and the underlying pathophysiology remains debated.

OBSERVATIONS: The authors describe the case of a 62-year-old male who presented with acute thoracic back pain and rapidly progressive unilateral lower limb weakness, evolving to paraplegia within hours. The initial deficit was highly atypical for a dorsally located compressive lesion, creating significant diagnostic uncertainty. Imaging revealed a T5-7 dorsal arachnoid web, which was considered an incidental finding given the atypical presentation. Subsequent imaging demonstrated web enlargement and the development of an owl's-eye T2 hyperintensity, indicative of anterior spinal cord ischemia. Emergency surgical decompression and arachnolysis were performed, leading to partial neurological recovery.

LESSONS: This case challenges the conventional understanding of SAWs as slowly progressive lesions and highlights the diagnostic complexity introduced by atypical presentations. The location of the web in a vascular watershed zone of the midthoracic spine likely contributed to the development of cord ischemia, which was suspected to be the primary driver of the patient's fulminant course. This case underscores the importance of considering SAWs in the differential diagnosis of acute myelopathy. https://thejns.org/doi/10.3171/CASE2682.