Table 1. Summary of the key findings of the case.

S100: a protein family that's soluble in 100% ammonium sulphate at a neutral pH; CD: cluster of differentiation; AE1/3: antibody cocktail used to indicate carcinomas; SMA: spinal muscular atrophy; Pax5: a B-cell specific activator protein; Mum1: multiple myeloma oncogene-1

Key Findings
Presenting Symptoms	Chronic back pain with progressive weakness in bilateral lower limbs.
Review of Systems	Denied fever, loss of consciousness, and headaches.
Red Flags	Progressive weakness with recent rapid deterioration, nonambulatory, young age, bilateral leg numbness, micturition difficulty, increased constipation, and loss of sensation below T10.
Imaging	Contrast-enhanced MRI of the spine.
Diagnosis	Spinal cord compression secondary to unknown mass lesion.
Treatment	Laminectomy and thoracic spinal cord decompression with lesion excision.
In-House Pathology Results	Unknown etiology, non-neoplastic cyst with mixed lymphoplasmacytic and histiocytic infiltrate.
Mayo Clinic Pathology Results	Unknown etiology, non-neoplastic cyst with mixed lymphoplasmacytic and histiocytic infiltrate.
(+) Biomarkers	S100 and CD68.
(-) Biomarkers	AE1/3, CD20, SMA, Pax5, CD30, CD15, Mum1, CD34, CD3, Desmin, Langerin, and CD1a.