Hemorrhagic pseudo-cystic transformation of a sequestered lumbar disc fragment mimicking a synovial cyst

• Sequestered disc fragment mimicking hemorrhagic synovial cyst. • MRI features suggested juxtafacet cyst with nerve root compression. • Histopathology confirmed discogenic origin with hemorrhage. • Radiological–pathological discrepancy highlighted. • Implications for surgical planning and prognostic interpretation. Background: Lumbar synovial cysts are most common in older adults, especially females, often associated with degenerative spine changes like facet joint arthritis and instability. Rarely, sequestered disc fragments may undergo hemorrhagic pseudo-cystic transformation and mimic synovial cysts on imaging. A 74-year-old female patient presented to the emergency department with acute lumbar pain radiating to the left groin and thigh. Magnetic resonance imaging showed a well-defined lesion adjacent to the left L2/3 facet joint, initially interpreted as a hemorrhagic synovial cyst with compression of the affected nerve root. At surgery, the lesion consisted of a dark, organized hemorrhagic mass. There was no cyst wall and no synovial connection. Histopathological examination, independently confirmed by three pathologists, demonstrated degenerated nucleus pulposus tissue with hemorrhage and granulation tissue, consistent with a sequestered disc fragment with secondary hemorrhagic transformation. Hemorrhagic pseudo-cystic transformation of sequestered disc material may mimic synovial cysts radiologically and intraoperatively. Histopathological confirmation is essential for accurate diagnosis and appropriate prognostic interpretation.