Ultrasound
What is the differential diagnosis?
Given the imaging appearance and continuity with the femoral nerve, this is likely a nerve sheath tumor such as a schwannoma or neurofibroma.
Where are the most common locations of schwannomas?
Schwannomas can occur in any nerve, most often seen in cranial nerves, with the vestibulocochlear nerve (CN VIII) being the most frequent site. They also commonly occur in the spinal nerve roots, as well as in intraorbital, brachial plexus, lumbosacral plexus, and limb locations, especially on flexor surfaces like the ulnar and peroneal nerves.
What are some imaging signs associated with schwannomas?
Some helpful signs in MRI diagnosis of schwannomas/nerve sheath tumors include the target sign which is high peripheral and low central signal on T2 imaging, the fascicular sign that includes multiple ring-like structures, and the split-fat sign which is a thin peripheral area of fat seen along the long axis of the lesion.
What are some syndromes associated with schwannomas?
Schwannomatosis, neurofibromatosis type 2, and Carney complex are associated with multiple schwannomas.
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.