Presentation
The patient initially presented with generalized abdominal pain. Upon further investigation, the patient reported a history of right hip/groin pain with intermittent radiating pain down the right lower extremity for one year. She also reported occasional weakness and numbness in the right lower extremity. On physical exam, there was a positive Tinel's sign over the right groin.
Patient Data
CT of the abdomen and pelvis without contrast shows a round hypodense mass in the right pelvis adjacent to the psoas and iliacus muscles. The appendix is not associated with the mass. The femoral nerve appears continuous with the mass at both the proximal and distal aspects. There is a small left adnexal cyst. No other mass is identified.
MRI of the right pelvis without and with IV contrast confirms a circumscribed mass in the right pelvis. This is slightly hyperintense on T1 (relative to skeletal muscle), hyperintense on T2 (with a markedly hyperintense central portion), and demonstrates heterogenous enhancement with lobular central cystic degeneration/necrosis. The femoral nerve appears continuous with the mass at both the proximal and distal aspects. The course of the femoral nerve above the mass and femoral nerve below the mass is best traced on the T1-weighted images. The mass is located medial to the psoas muscle and anterior to the iliacus muscle. It indents these muscles without invasion. The common femoral vein and common femoral artery are medial to the femoral nerve / mass. There is no pelvic or inguinal lymphadenopathy.
Ultrasound shows a round circumscribed mass in the right pelvis with internal vascularity. This appears predominantly hypoechoic with some internal anechoic areas. There is acoustic enhancement deep to the mass. Ultrasound-guided core biopsy of the mass was performed with an 18-gauge biopsy device.
Case Discussion
Imaging depicts a circumscribed lesion medial to the right psoas muscle and anterior to the iliacus muscle. The lesion is heterogeneous with a nonenhancing central component and is hyperintense on T1 and T2-weighted imaging. The margins of the lesion appear smooth with no local invasion. The lesion has features suggestive of a right hemipelvic schwannoma involving the femoral nerve.
The pathology was consistent with a schwannoma. Spindle cells were seen which stained positive for S100 and SOX10, and negative for pankeratin. Surgical resection of the schwannoma was scheduled, but subsequently canceled due to pregnancy.
Peripheral nerve schwannomas account for 5% of all soft tissue neoplasms and can occur in association with neurofibromatosis type 2 and schwannomatosis or sporadically 1. On imaging, this is typically a well-defined mass with cystic degeneration seen in larger lesions. It may be associated with the target sign, fascicular sign, and/or split-fat sign 2. Malignant transformation is rare. Surgical resection is the primary treatment.
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