Lumbar Degenerative Spondylolisthesis and Synovial Facet Cyst With Adjacent Intradural Filum Terminale Lipoma: A Case Report

BACKGROUND: Spinal lipomas of the conus medullaris and filum terminale are the most common forms of occult spinal dysraphism. Clinical presentations vary based on anatomic location and size. Filum terminale lipomas occur in up to 5% of the general population based on cadaveric and magnetic resonance imaging studies. Most filum terminale lipomas are asymptomatic and rarely require treatment. CASE PRESENTATION: This is the first known reported case of a 64-year-old woman presenting with lumbar radiculopathy with cascading spondylolisthesis at L3 to L4 and L4 to L5, synovial facet cyst at L4 to L5, and concurrent large filum terminale lipoma. After nonoperative management strategies failed, an extensive discussion about the source of her symptoms was completed. It was believed that the primary driver of her radicular pain was the synovial cyst and spondylolisthesis at L4 to L5, despite the large size of the lipoma. Surgical treatment entailed an L4 to L5 anterior lumbar interbody fusion, posterior spinal instrumentation and fusion using robotic-assisted navigation, and decompression of the synovial cyst through a transfacet approach. Postoperatively, the patient's buttock and leg pain was resolved. She returned to work with no restrictions and reported no pain or neurological symptoms at her final follow-up. CONCLUSIONS: Incidental filum terminale lipomas may be safely observed when surgically managing a patient with a concurrent, adjacent, and symptomatic degenerative lumbar spondylolisthesis and synovial facet cyst. CLINICAL RELEVANCE: In patients undergoing surgery for symptomatic degenerative lumbar spondylolisthesis with an associated synovial facet cyst, an incidentally identified, adjacent intradural filum terminale lipoma without tethered cord symptoms can generally be managed nonoperatively, avoiding unnecessary intradural exploration and its associated risks.