A 30-year-old male patient presented with non-tender swelling on the ventral aspect of left distal forearm and hand since childhood, which was gradually increasing in size. He also complained of numbness and paraesthesias in the hand and fingers. There was no history of remote trauma.
Ultrasound (US) of the lesion showed thickened hypoechoic fascicles of the median nerve surrounded by echogenic fatty tissue. An MRI of the lesion revealed a grossly enlarged median nerve with thickened T1 and T2 hypointense nerve fascicles. These fascicles were surrounded by T1 hyperintense signal, which was suppressed in fat-saturated images, suggestive of fatty tissue. These findings were consistent with fibrolipomatous hamartoma (FLH) of the median nerve. Subsequently, the patient underwent surgery and nerve decompression by subtotal tumour excision. Histopathology confirmed the diagnosis of FLH.
FLHs are rare lesions in which there is abnormal proliferation of fatty tissue within nerves and fibrosis in the endoneurium and perineurium, which leads to formation of fusiform neurogenic mass lesions. Median nerve is the most commonly involved nerve, although other nerves such as ulnar, radial, peroneal nerves and brachial plexus may be involved [1,2]. Patients with such lesions usually present with a painless swelling along the course of the affected nerve in the third or fourth decade of life associated with paraesthesias and numbness [1]. Patients with FLH of the median nerve can present with symptoms of carpal tunnel syndrome[3]. Rarely, patients with FLH may have associated overgrowth of bone and fibrofatty tissue leading to macrodactyly; this condition is known as macrodystrophia lipomatosa[4].
In patients with FLH, US shows thickened hypoechoic nerve fascicles surrounded by hyperechoic fatty tissue resulting in coaxial cable-like appearance of the median nerve on transverse imaging. No internal vascularity is seen on doppler evaluation [1,5].MRI shows enlarged median nerve with T1 and T2 hypointense thickened nerve fascicles. There is surrounding T1 hyperintense signal which is suppressed on fat-saturated images, suggestive of fatty tissue. The appearance on coronal and sagittal images has been likened to spaghetti string, whereas on axial MR images, the lesion seems to have a coaxial cable-like appearance [6]. No enhancement is seen with contrast. These findings are consistent with FLH.
Electrophysiological studies such as nerve conduction velocity (NCV) and electromyography (EMG) are used in evaluation of peripheral neuropathies as they enable functional assessment. Sonoelastography is a relatively newer technique which helps in the early diagnosis of peripheral neuropathies based on changes in the stiffness of the involved nerve. However, since imaging is diagnostic in FLH, these studies are not indicated.
Most patients are managed conservatively, while others having symptoms of carpal-tunnel syndrome undergo decompression surgery for relief of symptoms[7].
Fibrolipomatous hamartoma of the median nerve
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This patient is a 30-year-old male who has had swelling in the left forearm and palmar (ventral) side since childhood, gradually increasing in size, accompanied by numbness and abnormal sensation in the hand and fingers. Ultrasound imaging shows that the lesion is located in the distribution of the median nerve, with a markedly thickened nerve bundle echo, a low internal echo, and surrounding high echo or fatty components, presenting a “coaxial cable-like” appearance on cross-sectional images. Doppler examination demonstrates no obvious abnormal blood flow signals. MRI indicates a significantly thickened nerve bundle in the range of the median nerve, showing low signal on T1WI and T2WI, with surrounding high T1 signal fatty tissue that is suppressed on fat-suppression sequences. The cross-sectional image also demonstrates a “coaxial cable” appearance, and the sagittal and coronal planes reveal a “spaghetti-like” imaging feature. No significant enhancement of the lesion is observed.
Considering the patient’s onset since childhood, progressive enlargement, imaging characteristics (thickened nerve bundles encased by fatty tissue, characteristic “coaxial cable” and “spaghetti-like” signs), and clinical symptoms (numbness and sensory disturbances), the most likely diagnosis is: Fibrolipomatous Hamartoma (FLH) Involving the Median Nerve.
If any clinical uncertainty remains, further tests such as EMG, nerve conduction velocity (NCV) studies, or histopathological biopsy may be conducted for definitive confirmation. However, based on the current information, FLH is strongly indicated.
For FLH patients, most can be managed conservatively, especially if symptoms are mild or there is no significant functional deficit, with regular follow-up. If nerve compression leads to prominent clinical symptoms (e.g., carpal tunnel syndrome) or functional impairment, surgical decompression can be considered:
Rehabilitation/Exercise Prescription (FITT-VP Principle):
During rehabilitation, it is crucial to proceed progressively and avoid excessive stretching or frequent flexion/extension that could aggravate nerve compression. If symptoms worsen, prompt reevaluation is recommended.
This report provides a reference analysis based on currently available data and does not replace in-person consultation or professional medical advice. If discomfort or worsening symptoms occur, please seek medical attention promptly.
Fibrolipomatous hamartoma of the median nerve
