Arachnoid cysts are benign masses that represent a relatively small percentage of intracranial lesions. Spontaneous rupture of an arachnoid cyst resulting in a subdural hygroma is a very rare event. We report a case of a pediatric patient with a history of an arachnoid cyst and chronic headaches presenting with bilateral papilledema, worsening headaches, and no history of head trauma. Magnetic resonance imaging of the brain revealed an extra-axial cystic lesion in the right middle cranial fossa, similar to an arachnoid cyst seen on previous imaging. A new right subdural collection similar to the cerebral spinal fluid signal causing mass effect on brain parenchyma was determined to represent a subdural hygroma. Craniotomy was performed to evacuate the subdural hygroma as well as cyst fenestration. We report this case to emphasize the importance of considering spontaneous rupture of an arachnoid cyst as a differential diagnosis despite absence of head trauma.

Myxoid liposarcoma is the second most common type of liposarcoma that typically presents in the lower extremities and has a predilection for men. Manifestation of this tumor in the lower back is rare. We report the first known case of an adult woman presenting with a soft tissue mass in her lower back. Following excision and further workup, the mass was positive for rearrangements of the DDIT3 (CHOP) gene at the 12q13 locus, consistent with the diagnosis of a myxoid liposarcoma. The tumor was noted to be intramuscular and extended into the margins, requiring re-excision at the previous resection site. Biopsy of the re-excised area was negative for evidence of residual myxoid liposarcoma. We report this case to highlight the importance of considering myxoid liposarcoma as a differential diagnosis in soft tissue masses presenting in the lower back.