Dumb-Bell Shaped Lipoma of the Sole: A Rare Case Presentation and Diagnostic Insight

INTRODUCTION

Lipoma is the most common benign soft tissue tumour found in the body. It is often referred to as a “universal tumour” due to its potential to appear anywhere in the body.^[1] Lipomas are composed of mature fat cells and are most commonly found in areas with abundant adipose tissue, which may explain why they are rarely found in areas like the palms and soles.^[2] The World Health Organisation (WHO) categorises lipomas, angiolipomas, and liposarcomas as adipocytic tumours and the largest single group of mesenchymal tumours of lipogenic differentiation.^[3] The exact aetiology and pathophysiology of lipomas remain unknown. They can develop in any area of the body that contains adipose tissue. Lipomas are observed to be four times more common in males than in females and are frequently seen in obese individuals between the ages of 40 and 60.^[4] The incidence of benign lipomas on the sole of the foot remains a rare clinical finding. Dumb-bell shaped lipomas have been reported under the zygomatic arch,^[5] in the mediastinum,^[6] in the spinal cord,^[7] pelvis,^[8] and on the sole.^[9] But the occurrence of such lipomas is very rare. This is a case report on a dumb-bell shaped lipoma on the plantar aspect of the foot.

CASE REPORT

A 60-year-old male presented to the surgery with a swelling over the plantar aspect of the left foot for 30 days. Swelling was of sudden onset, progressed in size over 30 days, and was followed by pressure changes over the area with the formation of an ulcer. There was no associated fever, discharge, or pain. On local examination, a 2 × 3 cm swelling was noted on the plantar surface with a central ulcer. The systemic examination was unremarkable. Magnetic resonance imaging (MRI) of the left foot revealed a well-defined, lobulated, dumb-bell shaped, fat-containing lesion epicentered in the plantar fascia, measuring 3.7 × 1.7 × 2.8 cm. The lesion extends across subcutaneous and intramuscular planes, involving the plantar muscles at the level of the shaft of the third and fourth metatarsals. It is inserted between the fourth and fifth flexor tendons without displacement or compression of adjacent structures. There were no features of abscess, osteomyelitis, or involvement of adjacent tendons or bones, with the possibility of it being a fibrolipoma [Figures 1 and 2]. The patient underwent a wide local excision of the lesion with the ulcer. The excised tissue was sent for histopathological examination [Figure 3]. This gave a diagnosis of lipoma. The postoperative period was uneventful. The operated site healed well with secondary intention. A 6-month follow-up showed no recurrence.

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Figure 1:

MRI Foot showing dumb-bell lesion in the plantar aspect of the midfoot involving both subcutaneous tissue and intramuscular planes. MRI: Magnetic resonance imaging.

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Figure 2:

MRI Foot showing a well-defined lobulated lesion. MRI: Magnetic resonance imaging.

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Figure 3:

Intraoperative image showing the specimen of wide local excision of the lesion with the ulcer.

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DISCUSSION

Lipomas occurring in the sole are rarely reported due to the lack of adipose tissue in this region.^[10] These benign tumours are typically characterised by slow growth and asymptomatic progression, often delaying clinical diagnosis. However, when present on the sole, they can significantly impair daily activities such as walking, resulting in considerable discomfort and functional limitation for the patient.^[11] While a presumptive diagnosis of lipoma is often made clinically, radiological evaluation becomes essential when the lesion presents with atypical features. Ultrasound and MRI are valuable tools in such scenarios, with MRI being considered the gold standard for evaluating soft tissue tumors.^[12] These imaging modalities are especially critical when the radiographic appearance is non-specific or when differentiation between lipoma variants (e.g., spindle cell lipoma, atypical lipoma, pleomorphic lipoma, lipoblastoma, angiolipoma) and liposarcoma is required. In such cases, definitive diagnosis is possible only through histopathological examination following surgical excision.^[7]

A particularly unusual and underreported presentation is that of a dumb-bell lipoma in the sole. To date, only a few cases have been described in the literature. Recurrence may result from the failure to identify and excise the deeper component of a dumb-bell lipoma, which may lie beneath the plantar fascia. Often, only the superficial portion is removed, leaving the deep-seated component undetected and unaddressed. Therefore, in cases of plantar lipomas, the possibility of a dumb-bell configuration should be strongly considered. MRI can aid in identifying components deep to the plantar fascia, ensuring complete excision and reducing the likelihood of recurrence.

CONCLUSION

Lipomas of the sole are uncommon due to minimal adipose tissue in this region, and dumb-bell variants are exceedingly rare. This case highlights the importance of thorough imaging, particularly MRI, in identifying deep-seated components of plantar lipomas. Complete surgical excision is critical to prevent recurrence. Clinicians should maintain a high index of suspicion for dumb-bell lipomas in recurrent or atypical plantar swellings to ensure optimal patient outcomes.