Challenges in diagnosing and treating lumbosacral dermoid cyst in an older patient: illustrative case.

backgroundLumbosacral dermoid cysts are rare pathological entities, particularly among adults, and can be challenging to diagnose because of nonspecific clinical symptoms and variable MRI characteristics. In this patient, the importance of including dermoid cysts in the differential diagnosis of lumbosacral intradural lesions, even in older patients, is highlighted. OBSERVATIONS: A 65-year-old woman presented with a 3-year history of progressive low back pain radiating to the left buttock and gait disturbance. She underwent mediastinal schwannoma resection under general anesthesia 22 years ago. Lumbar spinal MRI revealed an intradural mass lesion extending from the L2 to L5 levels with high and iso-hyperintense signals on T1- and T2-weighted images, respectively. The lesion was heterogeneously enhanced with gadolinium contrast. CT demonstrated calcifications at the L5 level. Without establishing a preoperative diagnosis, surgery was performed. Intraoperatively, a brownish capsule containing hair follicles and sebaceous material was dissected and removed from the lumbar enlargement and surrounding nerve roots. A small portion of the tumor remained inside of the conus medullaris. Postoperative MRI confirmed near-complete tumor resection, and the patient experienced symptomatic improvement. Histological analysis confirmed the diagnosis of dermoid cyst. LESSONS: Dermoid cysts typically contain hair, sebaceous material, and calcifications. Their capsule may adhere firmly to the spinal cord or nerve roots. Careful surgical manipulation is essential to prevent injury and subsequent chemical meningitis. Preoperative recognition of this pathology is crucial for surgical planning, patient counseling, and minimizing intraoperative risks. Awareness of this rare condition in older patients can lead to more accurate preoperative diagnosis and improved clinical outcomes. https://thejns.org/doi/10.3171/CASE25883.