Dark as night: Spelunking for spinal solitary fibrous tumors/hemangiopericytomas in the differential of T2 hypointensity.

Spinal solitary fibrous tumor/hemangiopericytoma (SFT/HPC) is a rare mesenchymal malignancy. Radiographically, SFT/HPCs have a mutable appearance, with irregular borders, heterogeneous contrast enhancement, and variable but frequently hypointense T2 signal. We report a series of 5 neurosurgically managed spinal SFT/HPCs treated at our institution, with particular attention to 3 lesions demonstrating marked T2-hypointensity and differential diagnosis for the unusual finding of a "T2 dark" spinal lesion. Retrospective chart review of prospectively maintained surgical database, queried by diagnosis and site codes, 2002-2017. Retrospective radiographic review, with initial screening via keyword search of MR reports for "T2" and "hypointense." Four primary and one metastatic spinal SFT/HPCs were operatively treated during the study period (median follow-up 12 months; range 10-92). Three demonstrated marked T2 hypointensity on preoperative MRI, underwent primary resection-GTR in two, STR in one-and have remained progression-free on routine postoperative surveillance. Two patients with isointense lesions recurred within the follow-up period. Radiographic review identified a host of predominantly rare T2-hypointense lesions, including arteriovenous malformation, disk fragmentations, calcific arachnoiditis, calcifying pseudoneoplasm of the neuraxis, cavernoma, cord hemorrhage/acute blood, desmoid, granulocytic sarcoma, pigmented villonodular synovitis, Edheim-Chester, extramedullary hematopoiesis, IgG4-negative inflammatory pseudotumor, idiopathic hypertrophic pachymeningitis, B-cell lymphoma, primary melanoma neoplasm, melanotic schwannoma, meningioma, opacification of the posterior longitudinal ligament, osteoblastoma, osteochondroma, osteosarcoma, and synovial cyst. T2 hypointensity is associated with SFT/HPC, and may be an indicator relative indolence. "Dark" T2 spinal lesions are rare, with a narrow differential populated predominantly by rare entities.