Purpose or Case Report: Fibrolipomatous hamartoma (FLH) of the median nerve, also known as perineural lipoma or lipomatous hamartoma, is a rare, slow-growing, benign neoplasm that arises from proliferation of fibrofatty tissue that infiltrates epineural and perineural elements and results in thickening of the axonal bundles. It is thought to be congenital, which is why many patients present in childhood, typically with painless enlargement of the distal forearm or volar wrist. Some patients may present with carpal tunnel syndrome because of median nerve compression. Macrodactyly of the involved region has been reported in rare cases. MRI is considered the preferred modality for diagnosis of FLH; however, ultrasound, computed tomography, and rarely, radiography also play important roles in diagnosis. Imaging allows for accurate differentiation of FLH from other disease processes such as peripheral nerve sheath tumor (PNST) and lipoblastoma. In symptomatic patients, treatment of FLH includes carpal tunnel decompression, fibrofatty sheath debulking, and microsurgical dissection of the neural elements. In asymptomatic patients, observation may be appropriate. This case series aims to describe multi-modality imaging manifestations of FLH presenting in children and highlight imaging features that are key to achieving a definitive diagnosis, sparing the need for surgical exploration and biopsy.

Case 1
11-year-old patient found to have a nontender, palpable mass in the right wrist. Radiographs revealed no abnormalities. Ultrasound of the palpable abnormality demonstrated an ovoid echogenic mass with internal hypoechoic fascicles contiguous with the median nerve, consistent with fibrolipomatous hamartoma of the median nerve. Patient has remained asymptomatic since diagnosis.

Case 2
12-year-old patient with numbness and tingling in the median nerve distribution. Ultrasound demonstrated an indeterminate heterogenous lesion in the wrist. MRI revealed a collection of enlarged cylindrical fascicles surrounded by fat along the course of the median nerve. The patient underwent carpal tunnel release with symptomatic relief. The patient developed enlargement of her thumb and soft tissue hypertrophy along the ulnar aspect from the thumb tip down into the webspace. Most recent MRI demonstrated stability of hamartoma; however, the patient has developed recurrent carpal tunnel syndrome and is scheduled to undergo neurolysis of the median nerve and debulking of the thumb tumor.
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