Subungual and Periungual Fibrolipomas Presenting with Nail Dystrophy: A Case Report and Literature Review

1. Introduction

Fibrolipoma is classified by the World Health Organization as a rare histologic subtype of traditional lipomas composed of mature adipocytes with fibrous connective tissue [1]. Lipomas of the nail unit are exceedingly rare because the onychodermis is fibrovascular and lacks a subcutaneous adipose layer [2]. Simultaneous subungual and periungual fibrolipomas have not been previously reported.

Preoperative diagnosis of nail unit lipomas is challenging because they mimic other nail tumors, including glomus tumor, subungual exostosis, and squamous cell carcinoma [3]. Imaging and histopathologic examination with immunohistochemical and molecular studies are essential for definitive diagnosis. We describe a case of simultaneous subungual and periungual fibrolipomas in a 59-year-old man, with emphasis on clinical, radiographic, and pathologic findings relevant to the podiatric physician.

2. Detailed Case Description

A 59-year-old man presented with a several-year history of a painless, nodular mass in the subungual and periungual regions of the right great toe. The affected nail plate showed marked thinning and onychodystrophy (Figure 1a). He reported no prior nail trauma or family history of similar conditions. Physical examination revealed swelling of the nail bed and distal phalanx with partial nail plate loss; the remaining nails were normal.

Radiography showed no phalangeal bone abnormality, although periarticular soft-tissue swelling was present without bone erosion. Ultrasound identified several nodules in the superficial soft tissue; the largest measured approximately 16 × 9 mm, with indistinct borders and irregular contour. Color Doppler imaging showed no significant internal vascularity. Surgical exploration revealed two well-demarcated, lobulated, yellowish, soft-tissue masses in the subungual and periungual areas; the lesions were not interconnected (Figure 1b-c).

Histologic examination showed mature adipocytes admixed with fibrous bundles and scattered plump spindle cells (Figure 2). Immunohistochemistry demonstrated partial S-100 positivity, focal p53 positivity, and a Ki-67 proliferative index of 2%; CD34, desmin, SMA, MDM2, and CDK4 were negative. Fluorescence in situ hybridization confirmed HMGA2 gene translocation without CDK4 or MDM2 amplification, establishing the diagnosis of fibrolipoma.

At 1-year follow-up after complete surgical excision, the surgical site had healed well with satisfactory nail plate regrowth from the proximal nail fold (Figure 1d). No recurrence was observed, and both function and cosmesis of the right toe were excellent.

3. Discussion

Fibrolipoma is an uncommon lipoma variant characterized by mature adipocytes with fibrous connective tissue [1]. Lipomas of the nail unit are exceedingly rare because the onychodermis lacks a subcutaneous adipose layer [2]. The simultaneous occurrence of subungual and periungual fibrolipomas in the same digit, as seen in our patient, has not been previously described.

A review of the literature identified 14 previously reported cases of nail unit lipoma, involving subungual (9 cases) and periungual (5 cases) locations, as summarized in Table 1 [2,5,6,7,8,9,10,11,12,13]. The mean patient age was 54.5 years, with a male predominance. Most lesions were painless, although some caused discomfort with footwear or mild movement restriction. All reported cases exhibited nail changes, including plate elevation, thinning, splitting, and dystrophy. Hao et al. [4] recently reported an eight-case series of toe lipomas, including one fibrolipoma, underscoring the relevance of this entity to podiatric practice.

Cytogenetic investigations have identified rearrangements involving the 12q14-15 region harboring the HMGA2 gene in a subset of lipomas [14]. An HMGA2 translocation was detected by FISH in our case, confirming a clonal chromosomal abnormality characteristic of benign lipomatous tumors.

Radiography is essential to exclude underlying bone lesions such as subungual exostosis [11]. In our case, plain radiographs showed no bone destruction. High-frequency ultrasound can define the soft-tissue architecture of the nail unit, with lipomas typically appearing as well-defined, homogeneously hyperechoic masses [6]. MRI is particularly valuable because adipose tissue exhibits characteristic high signal on T1- and T2-weighted images with signal suppression on fat-saturation sequences [15].

Definitive diagnosis requires histopathologic examination. Fibrolipoma is characterized by well-differentiated mature adipocytes partitioned by fibrous septa into a lobular architecture; myxoid stroma and lipoblasts are absent [1,15]. Immunohistochemistry typically shows partial S-100 positivity with negative CD34, desmin, SMA, MDM2, and CDK4 [15]. HMGA2 rearrangement and lack of MDM2 or CDK4 amplification, demonstrated by FISH, help exclude atypical lipomatous tumor or well-differentiated liposarcoma [15,16]. The differential diagnosis includes glomus tumor, subungual exostosis, epidermoid cyst, and squamous cell carcinoma [12].

Complete surgical excision is the treatment of choice for nail apparatus lipomas. Preservation of the nail matrix and germinal epithelium facilitates postoperative nail regrowth. All reported patients, including ours, have remained recurrence-free after excision, underscoring the excellent prognosis.

5. Conclusions

Subungual and periungual fibrolipomas are rare benign tumors that warrant inclusion in the differential diagnosis of painless subungual nodules with nail dystrophy. Accurate diagnosis requires clinical correlation, imaging, and histopathologic examination with immunohistochemical and molecular studies. Complete surgical excision offers excellent functional and cosmetic outcomes with minimal recurrence risk.