Fibrolipomatous Hamartoma Arising from the Median Nerve-A Case Report

Fibrolipomatous hamartoma is a rare nonhereditary, congenital condition characterized by benign hyperplasia of fibroadipose tissue around nerve bundles. The median nerve is commonly affected. Underlying pathological process is mature adipose and fibrous tissue infiltrating the epineural and perineural compartments giving typical "pseudo-onion bulb" appearance on histology and "coaxial cable" appearance on magnetic resonance imaging (MRI). This case of fibrolipomatous hamartoma well illustrates its characteristic clinical, radiological, and histopathological features. Patient is a teenage female presented with painless gradually enlarging mobile lump in the central left palm. Ultrasound scan revealed a hyperechoic subcutaneous lesion, with intervening fine hypoechoic cable like structures following the course of median nerve which was thickened. Computed tomography (CT) confirmed thickened left median nerve with radiating isodense fascicles surrounded by fatty areas. There were no calcifications. MRI showed classic "coaxial cable" like T1, T2 isointense fascicles continuous with the median nerve surrounded by a fusiform lesion demonstrating fat signals on spin-echo sequences which dropped on fat-suppressed gradient echo sequences. Diagnosis of fibrolipomatous hamartoma arising from left median nerve was made, based on typical imaging findings. Biopsy confirmed fibrolipomatous hamartoma. Diagnosis can be made confidently on imaging alone especially with MRI, without the need of biopsy. Both CT and MRI demonstrate fatty mass encasing the thickened nerve fibers. On MRI, characteristic appearance is seen as T1 and T2 low intense tubular thickened neural bundles surrounded by high signal fatty tissue.