Giant Lipofibromatous Hamartoma of Lower Extremity in a 6-Year-Old Child: A Location Seldom Encountered

Dear Editor, Lipofibromatous hamartoma (LFH) is a rare and benign tumor that grows slowly, primarily affecting the peripheral nerves.[1] Histologically, it is marked by fibrofatty alterations in the nerve, accompanied by perineural and endoneural fibrosis, as well as thickening of the nerve fascicles. While this tumor typically presents in 3rd decade of life, with symptoms pertaining to compressive neuropathy and exhibits a distinctive coaxial cable-like appearance on magnetic resonance imaging, which is pathognomonic for this entity, on the contrary, the present case was just a 6-year-old kid, having no neurological complaints and initially diagnosed as a diffuse lipoma on radiological examination.[2] This was a 6-year-old boy, hailing from a poor socioeconomic background who presented to the department of pediatric surgery with a recurrent huge lump over the right buttock and lumbar region. The mass was present since birth, initially of lemon size, and gradually progressed to the present size. A few years ago, when the lump was relatively small in size, it underwent excision and was diagnosed as a lipoma. The child had no history of trauma and had no neurologic complaints or any symptoms of compressive neuropathy. On clinical examination, the lump measured 8 cm ×6.5 cm ×4 cm, with regular borders and soft to firm in consistency [Figure 1a]. There were no sensory or motor deficits in the lower limb. Based on clinical examination, a diagnosis of a diffuse lipoma was given. Radiological imaging conducted at an external facility further corroborated the clinical diagnosis of lipoma. A wide local excision was done and sent for histopathological examination. On gross examination, the cut surface was yellow–gray and was lobulated; in the center of the lesion, the nerve was identified which was unevenly thickened and elongated [Figure 1b]. Histological examination revealed interwoven collagen, fibroblasts, mature adipocytes, intermittent capillaries, and focal myxoid areas [Figure 2a]. The nerve sheath was thickened with areas of fibrosis infiltrating the space between the epineurium and perineurium creating separation between nerve fascicles [Figure 2b-d]. Multiple nerve bundles showed concentric perineurial and endoneurial fibrosis, giving the appearance of pseudo-onion bulb [Figure 2e and f]. Immunohistochemical staining with S100 revealed compressed nerve fascicles encased by the tumor and in the surrounding adipocytes, while smooth muscle actin (SMA) staining accentuated the areas of fibro-neural hyperplasia. No mitotic figures, atypical cells, inflammatory cells, or myelin degeneration were noted in any of the foci. Thus, a final diagnosis of LFH was given. The child developed mild paraesthesia of the affected limb in a 9-month follow-up period [Figure 3].Figure 1: (a) Clinical image showing a large lump present over the right buttock and lumbar region, (b) Gross image showing yellow-gray, lobulated cut surface with an unevenly thickened and elongated nerve in the center of the lesionFigure 2: (a) Histological examination showing haphazardly arranged bundles of fibrous tissue, interwoven collagen, intervening adipose tissue, capillaries, and occasional myxoid areas (H and E, ×40), (b and c) Occasional thickened nerve bundles showing surrounded by accumulated fibrous tissue and collagen along with adipose tissue (H and E, ×100), (d) Microphotograph showing abnormal amount of fibrofatty tissue entrapping multiple nerve fascicles (H and E, ×100), (e and f) High power views showing prominent endoneurial and perineurial fibrosis (pseudo-onion bulb appearance) (×400)Figure 3: Immunohistochemical stains: (a-c) S100 immunohistochemistry highlighting the Schwann cells in nerve fascicules compressed by tumor, S100 positivity in the surrounding adipocytes (×400), (d-f) SMA highlighting the fibroneural hyperplasia (×40, ×400, ×400)LFH, an infrequent nerve tumor, typically emerges within the initial three decades of life and presents as an acrochordon, cutaneous cyst, or soft-tissue tumor.[3] The tumor commonly manifests as a palpable mass enveloping nerves in the upper limbs, resulting in pain, sensory disturbances, and motor deficits within the affected nerve distribution.[3,4] It is imperative for clinicians to recognize this disorder, as untreated cases may progress to nerve compression, eventually leading to peripheral neuropathy. Histologically, the tumor is primarily composed of fat and fibrous tissue, featuring epineural and perineural proliferation. While the median nerve and its branches are frequently affected, literature documenting the involvement of ulnar, radial, and lower limb nerves (plantar, peroneal, and sciatic) remains limited.[5] This was clearly elucidated by Silverman and Enzinger’s report, in which out of 26 cases, 25 were identified in the hand and wrist (median nerve involvement in 22 instances), with only one case noted in the foot.[6] The lesion is classified as a hamartoma due to the excessive proliferation of normal connective tissue components, specifically fat and fibrous tissue. Histopathological analysis reveals infiltration of the epineurium by fibrofatty tissue, which dissects and compresses the nerve fascicles. This infiltration leads to neural atrophy, frequently accompanied by pronounced perineural fibrosis. Chronic changes such as axonal degeneration and collagen deposition are also evident. A pseudo-onion bulb-like hypertrophic pattern arises as a result of increased perineural cell proliferation. This tumor is frequently misidentified as diffuse lipomatosis, traumatic neuroma, fibromatosis, intraneural lipoma, hemangioma, plexiform neurofibroma, and ganglion cyst. Considering the large size of tumor in the present case differentiation from malignant conditions, such as liposarcoma and malignant peripheral nerve sheath tumor, was also necessary. The above mentioned differentials can only be distinctly discerned through histopathological examination. LFH is an infrequent condition typically seen in younger individuals, with a tendency to affect nerves in the upper extremities. While the characteristic imaging features are usually present, in rare instances, they may not be conclusive. In such cases, histopathological examination becomes crucial. Over time, the lesion may lead to nerve compression, potentially culminating in the development of peripheral neuropathy. Declaration of patient consent The authors certify that they have obtained all appropriate consent forms, duly signed by the parent(s)/guardian(s) of the patient. In the form, the parent(s)/guardian(s) has/have given his/her/their consent for the images and other clinical information of their child to be reported in the journal. The parents understand that the names and initials of their child/children will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.