Fibrolipomatous hamartoma (FLH) is a rare congenital benign tumor that can present in childhood or adulthood ^[1]. Although infrequent, there are reports of affection of the median nerve, the radial or ulnar nerves of the upper limb, and the sciatic or plantar nerves of the lower limb [2-6]. The degree and length of the nerve affected determine the symptoms.

A male patient in his mid-20s presented to the outpatient department with 4 months of swelling over the volar aspect of the left forearm and hand. The swelling was insidious in onset, which initially started as a forearm swelling and slowly progressed into the palm with a gradual increase in size. The patient complained of tingling and numbness over the palm and radial 3½ fingers (middle, index, and thumb fingers) with pain on excessive limb use. There was no history of fever or trauma preceding the onset of the swelling. No other swellings are present elsewhere. A continuous, soft, non-tender, non-compressible, immobile, smooth swelling measuring 6 × 4 cm was evident over the flexor aspect of the left forearm extending from the distal third of the forearm to the proximal palmar crease (figure 1a, b). Along the course of the median nerve, Tinel’s sign was positive at the wrist and radial three and a half fingers. Both Phalen’s and Durkan’s tests came back positive, pointing to possible median nerve compression at the carpal tunnel level. The wrist and fingers were moving usually.

On electromyography, there was a delay in nerve conduction. Magnetic resonance imaging (MRI) was suggestive of the swelling arising from the median nerve abutting the flexor musculature passing through the carpal tunnel and involving the palmar cutaneous branch (figure 2a, b). The patient was counseled for surgical excision.

Intraoperatively, the tumor encapsulated the median nerve and the  nerve was edematous (figure 3a). Under microscope, the capsule was opened, revealing the grayish to bluish–white substance dispersed around and involving the fascicles. The tumor could not be removed separately from the nerve substance. A segment of a cutaneous branch of the median nerve was sent for histopathological examination. Decompression of the carpal tunnel was performed with debulking of fibrofatty elements and fine dissection of the neural elements (figure 3b).

Histopathology revealed lobules of adipocytes and bland fibrosis with ropy collagen deposition entrapping the nerve. The fibromatous or lipomatous component did not show any nuclear atypia or other features of malignancy suggestive of FLH (figure 4a, b).

Postoperatively, the patient was on temporary splintage for a week and physiotherapy was performed for 3 months. At 6-month follow-up, the patient was completely free of symptoms. There was no weakness or loss of sensation in the involved limb.

FLH is a relatively rare but benign condition. The exact etiology is unknown, but the hypertrophy of mature fat and fibroblasts in the epineurium has been postulated ^[7]. FLH of the median nerve presents as a fusiform swelling of the nerve itself rather than a clearly defined swelling coming from the nerve ^[8]. Opening the epineurium revealed no obvious edema. We found that fascicles were enlarged, suggestive of a tumor, and the nerve material appeared gray to bluish. The swelling, which was palpable and well-defined swelling was not seen intraoperatively but rather fibrofatty tissue merging with the fascicles, giving the nerve a fusiform look. FLH can have neuropathy symptoms as it is attached to the nerve and increases in size ^[9]. The intraneural spread of the tumor itself is not the cause of these symptoms but depends on the severity of the compression. Involvement of the median nerve will give rise to carpal tunnel syndrome (CTS), and there are cases of macrodactyly also reported ^[10]. When it affects other parts body, such as the neck, and lower limb, it can give brachialgia or sciatica. Few reports involving the radial or ulnar nerves have also been described [11, 12]. The gold standard of investigation is MRI ^[5]. The MRI findings are quite pathognomonic, which helps to differentiate from other benign tumors ^[13]. On T1-weighted images, it appears as low-signal nerve bundles encircled by high-signal fibrolipomatous tissue ^[14]. A conspicuous increase in adipose tissue in a fibrous network that involves the nerve sheath, muscles, and subcutaneous tissue is characteristic. Adding a diffusion-weighted imaging sequence in association with conventional MRI improves the diagnosis ^[15]. FLH can be managed conservatively, and few require surgical exploration ^[16]. The characteristic MRI findings do not make the biopsy prudent before surgery ^[10]. Medications such as pain relievers or anti-inflammatory drugs may be prescribed to manage pain and inflammation associated with FLH. Surgery is indicated for symptomatic benign lesions ^[11]. Often, the FLH is seen to encompass the nerve root, and therefore, complete enblock excision may not be possible without grafting. Piecemeal decompression should suffice. Sarp and Pekcevik have reported internal neurolysis for a case report of giant lipomatosis of the sciatic nerve ^[6]. The details of reported cases and their management are elaborated in Table 1. Debulking of the lesion is possible, but extensive intraneural dissection runs the risk of ischemic consequences. Some authors recommend complete excision of the mass along with nerve repair, however, this can cause significant neurological damage ^[24]. Therefore, we advocate precise and careful intraneural dissection under a microscope with higher magnification.

It’s crucial to note that treatment decisions should be individualized based on the specific characteristics of the FLH and the patient’s overall health. Extensive intraneural dissection has a risk of ischemic complications. Some authors recommend complete excision of the mass along with nerve repair; however, this can cause significant neurological damage. Microsurgical separation of the neural components under the microscope with higher magnification, followed by carpal tunnel release, was sufficient in our case of FLH encompassing the median nerve and producing symptoms of CTS.

FHL is a benign condition. The presentation is usually asymptomatic until there is a compression of the nerve rather than intraneural involvement by the tumor. A thorough clinical and radiographic assessment is required to diagnose this uncommon lesion. Lipomatosis of the nerve is not precisely or consistently treated. Microsurgical dissection of the neural components under a microscope and post-operative care and physical therapy can produce positive outcomes when decompression is not an option.