Sciatic Nerve Schwannoma in the Lower Limb Mimicking Ganglion Cyst.

We present the case of a 49-yr-old woman with a 2-mo history of right lower limb pain radiating to her foot. The back of the right lower limb was touched with a jujube-like mass. On physical examination, both lower limbs were negative in the active straight leg raise test. The lower limb skin was normal but sensitive to pain, and the knee and heel tendon reflexes were normal in the neurologic examination. Ultrasound scanning revealed enlargements and effusions in the sciatic, tibial, and common peroneal nerves and hypoechoic nodules in the epineurium of the sciatic nerve, with a blood flow signal inside. A computed tomography scan with contrast revealed a significantly enhanced sciatic nerve nodule with no enhancement in the diffuse nerve bundle. Magnetic resonance imaging revealed cystic fluid displaying a water signal intensity that expanded to the tibial and common peroneal nerves, with apparent enhancement on contrast imaging; low-medium signal intensity on the T1-weighted image and high signal intensity on the T2-weighted image were observed in the lower sciatic nerve along with a thickened epineurium (Fig. 1). The patient underwent surgical resection, with the removal of a 30 × 20 × 20-mm, gray-white, encapsulated mass adhered to the peripheral nerve bundles (Fig. 2). Histopathological examination showed crowded spindle cells with palisading nuclei in Antoni A areas, supporting the diagnosis of a sciatic nerve schwannoma. At follow-up 1 mo later, the patient reported the disappearance of the radiating pain, and a magnetic resonance imaging showed no effusion in the nerve bundles and no residual tumor.

FIGURE 1

Magnetic resonance imaging showed thickening and effusion of the right sciatic nerve bundle (white fine arrow), suspected schwannoma located between the sciatic nerve bundles, and deformation under pressure (white thick arrow).

FIGURE 2

Intraoperative view.

Schwannomas originate from Schwann cells in the nerve sheath. Schwannomas are commonly found in patients aged 20–50 yrs in the head and neck region.[1] However, it is sporadically observed in the sciatic nerve; hence, the diagnosis might be challenging.[2] Schwannomas typically present with an enlarging soft tissue mass, although the patient would not experience acute or radicular pain until the tumor becomes large enough to squeeze the nerve roots.[3] Schwannomas are hard to differentiate from ganglion cysts that present with similar clinical symptoms along with cystic fluid that commonly accumulates in the adjacent articular space. In addition to locating the lesion, magnetic resonance imaging is recognized as an effective means to diagnose a schwannoma or ganglion cyst. A magnetic resonance imaging outlines the size, shape, edge, and surrounding edema of the lesion, helps understand whether the adjacent blood nerves are invaded, and aids in making an accurate diagnosis based on the changes in signal intensity.[4] Even if the tumor capsule is fragile or adherent to surrounding tissues, surgical excision is recommended to treat a sciatic nerve schwannoma. In conclusion, an accurate differential diagnosis of a sciatic nerve schwannoma could reinforce the management of this disease and improve the patient’s prognosis.