Introduction

Spindle cell lipoma (SCL) is a benign mesenchymal neoplasm first described in 1975 by Enzinger and Harvey as a subtype of lipoma (1). It typically presents as a slow-growing, painless subcutaneous mass, most often in middle- aged to elderly men. Common sites include the posterior neck, shoulder, and upper back, while rare manifestations have been reported in the oral cavity, parotid gland, breast, and extremities (2, 3). SCL involving the inguinal canal is particularly uncommon and may clinically mimic inguinal hernias, liposarcomas, or lymphadenopathies, posing diagnostic difficulties both clinically and radiologically.

Accurate diagnosis of SCL relies on histopat-hological and immunohistochemical features that distinguish it from other soft-tissue tumors. Characteristic features include uniform spindle cells, mature adipocytes, and dense collagen bundles, typically expressing CD34 while being negative for S‑100, Desmin, and other lineage markers (4). In this report, we present a rare case of inguinal SCL in a 68‑year‑old man, initially misinterpreted as a probable hernia. The lesion was surgically excised and confirmed histologically as SCL. Notably, follow‑up imaging demonstrated complete resolution without recurrence, emphasizing the benign behavior of the tumor and the value of comprehensive diagnostic evaluation.

Case Presentation

A 68‑year‑old man presented to the surgical clinic with a 2–3‑month history of a right inguinal swelling extending into the scrotum. The patient reported progressive enlargement of the mass, which reduced in the supine position but reappeared when standing or during physical activity. He also complained of lower abdominal discomfort and urinary symptoms, including weak stream, frequency, dysuria, and nocturia. He was receiving tamsulosin at the time of assessment. His past medical history included type 2 diabetes mellitus and ischaemic heart disease (post‑angioplasty one year earlier). He had previously undergone three transurethral lithotripsy (TUL) procedures. There was no history of drug allergy, family history, or other systemic illness. On examination, a non‑tender, soft mass was palpable in the right inguinal canal without signs of inflammation. Scrotal contents were otherwise normal, and no features of inguinal or femoral hernia were noted.

Baseline laboratory investigations, including CBC, renal function tests, PSA, and urinalysis, were unremarkable except for 2+ blood in the urine. Tumour markers were within normal limits. Further imaging was conducted. CT of the abdomen and pelvis with contrast revealed a soft‑tissue lesion measuring approximately 50 × 38 mm in the right inguinal canal, surrounded by fat stranding but without lymphadenopathy or solid‑organ involvement. Scrotal ultrasound and inguinal Doppler demonstrated no hernia and no significant lymph node enlargement, though a few small reactive nodes (<12 mm) were observed. Similarly, pelvic MRI showed no abnormalities in the pelvic organs, vasculature, or bony structures (Figure 1). A bone scan excluded osseous metastasis.

Figure 1: Pelvic MRI showing no abnormalities in the pelvic organs. Histopathological examination revealed bland spindle cells with mature adipocytes and eosinophilic collagen bundles. 

The patient underwent surgical excision of the lesion. Gross pathology showed a well‑circumscribed, yellowish, firm mass measuring 6 × 4 × 3.5 cm. Histopathological examination revealed bland spindle cells with mature adipocytes and eosinophilic collagen bundles, without cytological atypia or mitotic activity. Immunohistochemical (IHC) studies demonstrated positivity for CD34 and a low Ki‑67 proliferation index (<1%), while SMA, HMB‑45, Desmin, and S‑100 were negative. The findings confirmed the diagnosis of spindle cell lipoma. Serial imaging during the two‑year follow‑up period, including CT and ultrasound, confirmed complete radiological resolution of the lesion, with no evidence of recurrence. (Figure 2).

Figure 2: Intraoperative finding of a well-circumscribed, yellowish, firm mass.

 Discussion

Spindle cell lipoma (SCL) is an uncommon benign adipocytic tumour that generally occurs in middle‑aged to older men, most frequently in the posterior neck, back, or shoulder region (5). First described by Enzinger and Harvey in 1975, SCL accounts for less than 1.5% of all lipomatous tumours and is characterised histologically by a mixture of mature adipocytes and uniform spindle cells arranged in a collagenous stroma (1, 6). Though well recognised histopathologically, its occurrence in uncommon anatomical locations may complicate diagnosis (5).

Inguinal SCL is particularly rare (7). In the present case, the progressively enlarging inguinal–scrotal mass initially raised suspicion of an inguinal hernia or malignant neoplasm. Absence of bowel or omental content on imaging excluded a hernia, while the lack of significant enhancement and lymphadenopathy reduced the likelihood of malignancy. Nevertheless,
fat stranding around the lesion and its deep pelvic extension warranted surgical excision and histopath-ological confirmation. Histologically, SCL contains mature adipocytes and spindle cells arranged in short fascicles separated by dense collagen bundles (8).

Immunohistochemical markers are key for diagnosis: spindle cells typically express CD34 and are negative for S‑100, Desmin, and SMA, distinguishing them from neural, myogenic, and atypical lipomatous tumours (9).

The low Ki‑67 index in this case supports the indolent nature of the tumour. The primary treatment for SCL is complete surgical excision, which is curative in most cases. Recurrence is rare and generally occurs only following incomplete excision (3). The absence of residual lesion in sequential imaging over two years strongly supports the benign character of the tumour and the success of surgical management.

This case further highlights the importance of long‑term follow‑up, particularly in tumours arising in atypical anatomical sites. Although benign, such lesions may mimic malignancies and thus require careful histopathological and immunohistochemical evaluation. Their presentation in regions such as the inguinal canal may also cause functional disturbances (e.g. urinary symptoms, discomfort on movement), justifying excision even in the absence of malignancy.

Only a limited number of SCL cases originating in the inguinal or para‑testicular region have been documented, most presenting similarly-with groin or scrotal masses misdiagnosed as hernias or malignancies. Table 1 summarises representative cases published in the last two decades. Most patients were older males who underwent surgical excision following suspicion of neoplasm or hernia. Histopathological and IHC findings consistently confirmed benign SCL, and long‑term outcomes were favourable, with no recurrence or metastasis.

Conclusion

This case illustrates a rare presentation of spindle cell lipoma in the inguinal canal, clinically mimicking an inguinal hernia. Imaging, surgical excision, and histopathological examination were all crucial for establishing the final diagnosis. Long‑term follow‑up confirmed the absence of recurrence, reaffirming the benign course of this tumor. Clinicians should consider SCL in the differential diagnosis of atypical soft‑tissue masses in the inguinal region, particularly in middle‑aged or elderly male patients.

Declaration

Acknowledgments

The authors extend their appreciation Sekineh Kamali Ahangar, the esteemed specialist of the Clinical Research Development Unit at Shahid Beheshti Hospital.

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