Complex surgical reconstruction for spinopelvic instability caused by a giant Tarlov cyst eroding the sacrum: A case report.

Background: Tarlov cysts (TC), also known as perineural cysts are meningeal dilations of the posterior nerve root sheath that typically affect sacral nerve roots. TC are usually asymptomatic and found incidentally. We present the case of a patient with an enlarging sacral TC causing pain from spinopelvic instability secondary to extensive bone erosion. Such illustrative case is intended to increase awareness of the potential need for complex spinopelvic reconstruction in atypical instances of large TC. Case Description: A 29-year-old female presented to clinic reporting progressive bilateral sacroiliac joint pain that was essentially mechanical in nature. The patient had a normal neurological exam except for a known left drop foot with numbness in the left sural nerve distribution, both attributed to a previously resected peripheral nerve sheath tumor. Magnetic resonance imaging revealed a large multilobulated lesion with imaging characteristics consistent with TC adjacent to the left side of the sacrum, extending outward from the left S1 and S2 neural foramina and measuring 6.7 × 3.7 cm in the axial plane and and 5.6 cm in the sagittal plane. Six weeks of conservative management consisting of physical therapy and pain management was unsuccessful, and the patient reported worsening pain. Surgical reconstruction consisting of L5-S1 transforaminal lumbar interbody fusion, L4 to pelvis navigation-guided instrumentation and posterolateral fusion, and bilateral sacroiliac joint fusion was successfully performed. Outcomes: At 12 weeks follow-up appointment after surgery, the patient reported resolution of sacroiliac mechanical pain. Conclusions: Sacral TC are asymptomatic in their vast majority of cases but may occasionally cause neurological deficits secondary to mass effect. Rarely, however, giant TC can also lead to significant bone erosion or the sacrum with secondary spinopelvic instability. In this brief report, we describe a giant TC generating significant spinopelvic instability, which was successfully treated with complex spinopelvic reconstruction, leading to complete resolution of the reported axial mechanical pain.