Original Article

Introduction

ipofibromatous hamartoma is a very uncommon, benign slow-growing peripheral nerve tumor^1–6 first reported by Mason in 1953.⁷ Macroscopically, the tumor appears as a fleshy yellow mass composed of the nerve with fibrofatty strands invading the epineurium. Microscopically fibrofatty elements of the tumor invade the peri- and endoneurium, separating the individual nerve fibers or groups of fibers. The tumor is probably a hamartoma since the fibrous, fatty and neural elements are essentially mature.^2–4This tumor is most often found in the median nerve with a predilection for the carpal tunnel.⁶

This report describes a rare case of secondary carpal tunnel syndrome due to a lipofibromatous hamartoma of the median nerve.

Case Report

The 25-year-old female patient who was diagnosed with carpal tunnel syndrome experienced numbness in her right middle finger for a few weeks prior to her admission. For several years, she had right wrist pain, nocturnal paresthesia, and paresthesia in the median nerve territory. Both the Tinel’s sign and Phalen test were positive. Additionally, the right thumb and thenar prominence were abnormally enlarged. According to the patient, the thumb macrodactyly had a constant volume for several years. There was no visible swelling at the wrist and distal forearm. Ultrasonography of the carpal tunnel did not provide a diagnostic clue, however, an electrophysiological study confirmed severe carpal tunnel syndrome. There was no café-au-lait spot or other signs of neurofibromatosis.

Under regional block, the patient underwent an open carpal tunnel release. After dividing the palmar fascia, there was a bulging of fatty tissue at the distal edge of the transverse carpal ligament. Following division of the transverse carpal ligament, an enormously enlarged median nerve infiltrated by fatty tissue was observed. The skin incision continued above the wrist crease. The abnormal tumoral appearance of the median nerve was located about five centimeters proximal to the wrist and extended to the beginning of the digital branches (Figure 1). The tumoral fat was without an obvious capsule and infiltrated into the nerve. There was a thick epineurinom that surrounded the nerve. An epineurotomy was performed which revealed a severely infiltrated fatty tissue and fibroses between the nerve fascicles. Excision of the fatty tissue between the nerve fascicles was impossible without the risk of incurring damage to them. Therefore, the tumor was left intact, and the operation was limited to a transverse carpal ligament release and epineurotomy. A small piece of the tissue was removed for histological examination; which showed fibrofatty elements of a tumor with an indefinite lobular pattern separating the nerve fascicles and fibers (Figure 2). Six months after surgery, the patient had marked improvement in her symptoms and there was no increase in tumor size. The term lipofibromatous hamartoma best describes the nature of this tumor.

Figure 1. The intra-operative view of the lipofibromatous hamartoma of the right hand’s median nerve of the patient

Figure 2. The histopatological view of lipofibromatous hamartoma of the right hand’s median nerve (H&E, ×100)

Discussion

Lipofibromatous hamartoma differs from a true lipoma of the median nerve; which is a soft encapsulated tumor that is easily shelled out from the surrounding tissue and contains no neural elements.²

The cause of lipofibromatous hamartoma is unknown, however, a congenital or developmental origin is likely since a majority of the tumors are present and manifest at a young age.⁴ In a majority of cases the median nerve is involved. The strong predilection for the median nerve is unexplained.¹Usually the first symptoms are paresthesia and carpal tunnel syndrome. MRI imaging is an important tool for pre-operative evaluation and findings are characteristic to provide a diagnosis.^8–10 Lipofibromatous hamartoma of the median nerve is commonly associated with macrodactyly.^1,2

There are two broad categories of tumors that can compress a peripheral nerve including the median nerve at the carpal tunnel: tumors with a neural sheath origin and those that have a non-neural sheath origin. Those tumors originating from the non-neural sheath include some rare benign and malignant tumors such as ganglions, hemangiomas, and lipomas, to name a few. The treatment of this type of lesion is usually straightforward and its complete excision can provide a cure. However, complete excision of an intra-neural tumor may not be feasible and can give rise to a neurological deficit.¹¹

The treatment of lipofibromatous hamartoma is highly controversial. Given the absence of symptoms and lack of major deformity, a wait and see approach is recommended.⁹

Infiltration of fibrofatty tissue between the nerve fascicles excludes complete excision of the abnormal tissue. Resection of the involved portion of the nerve results in various degrees of neural deficit and seems to be unnecessary.⁴ Therefore, complete excision of the tumor can be achieved at the cost of sacrificing the nerve and is usually contraindicated.⁹

Louis et al. observed slow but progressive loss of nerve function in a long-term follow-up of four patients.³ Houpt et al. advocated complete excision along with nerve grafting in children and an immediate tendon transfer in adults.¹²Some authors had a satisfactory outcome after decompression of the median nerve by dividing the transverse carpal ligament.^1,2

This case is presented because of its rarity.

Awareness of the existence of such a rare tumor and the development of carpal tunnel syndrome may lead to better evaluation, management and understanding of similar soft tissue lesions.

Conflict of interest statement

There is no conflict of interest of any kind in preparing this manuscript.

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