Lipoma defined as a ubiquitous swelling is a usual soft-tissue swelling and represents about 50% of all soft-tissue swelling ^[1]. One-fourth of soft-tissue swelling is generally malignant ^[2]. Lipoma is rarely found in the sole. This is because it comprises mature fat cells that are typically discovered in regions where there is rich adipose tissue [2, 3]. Per our literature search, such a case has not been reported in Ghana and the sub-region even though lipoma occurring in other parts of the body have been reported ^[4] The rare nature of a lipoma found at the plantar surface of the foot makes this case fascinating and the creation of awareness can help heighten the index of suspicion among clinicians.

A 49-year-old female teacher with no history of chronic illness referred on account of painless swelling on the sole of the left foot of 2-month duration. The swelling had gradually increased in size over the period. She had no history of trauma to the left foot before the development of the swelling. Before the presentation, a Doppler ultrasound done revealed fluid collection in the subcutaneous tissue of the plantar of the left foot with mixed echogenicity measuring about 2.6 × 2.5 × 1.8 cm (Vol. 6.0 mL). The surrounding soft tissue demonstrated areas of inflammatory changes. Hence, an impression of the abscess was reported with a queried diagnosis of hematoma. X-ray of the left foot was unremarkable. On examination, there was a 5 cm × 3 cm swelling at the medial arch of the left foot. The mass was soft, tender, not mobile, and attached to the overlying skin. The slip sign was note licited. The overlying skin was hyperkeratotic (Fig . 1). There were no palpable inguinal lymph nodes. Based on history, physical examination, and investigations, the patient was prepared for an excision biopsy. A popliteal block was given, and a tourniquet was applied. Under aseptic conditions, an s-shaped transverse incision was made over the swelling and deepened to the capsule of the mass. There was a fatty-looking mass extending from the medial arch of the foot to the base of the second toe. The mass was excised and hemostasis was secured and the incision was closed in layers with vicryl 2.0 to subcutaneous tissue and prolene 2.0 to skin and a dressing was applied. The post-operative period was unremarkable. The stitches were removed post-operative day 14. The histopathological report revealed microscopically an area showing lobules of mature fat cells with areas of fibrous septae which have blood vessels and some nerves. A definite diagnosis of fibro lipoma with no malignancy was made. The patient was reviewed at the outpatient clinic. A 6-month follow-up period showed a healed wound and the patient can fully step on her left foot.

Lipomas are benign swelling, representing about 50% of all soft-tissue swelling [1, 5]. These swellings are uncommon on the foot, representing about 4% of benign tumors. Lipoma usually occurs where fatty tissues are found. They are benign and mesenchymal neoplasms ^[11]. These swellings usually affect the shoulder, upper back, trunk, and neck ^[8] which disagrees with our case report whereby the lipoma was on the sole. Ozdemir et al. as cited by Dholakia et al. examined case series of 196-foot tumors and described the most common of them was ganglion after which plantar fibromatosis followed; lipoma accounted for (2%) with just four cases [6, 11] Lipomas usually occur in the 4th–7th decades of life and this patient fits into the age category for lipomas [11, 12]. Furthermore, lipomas are often found in patients who are obese [5, 13] which disagrees with our findings since our patient was in the overweight category with a body mass index of 25.7. The etiology of lipoma remains uncertain [8, 14] like in our case report; however, a many risk factors may include genetic aberrations, obesity, hypercholesterolemia, and trauma [1,10]. Post-traumatic lipoma can result from herniation of fatty tissue after trauma. This is a pseudo lipoma as it is not a real tumor of the adipose tissue ^[1]. Inflammatory cytokines and mediators released by traumatized and dead cells can lead to the differentiation of pre-adipocytes to mature adipocytes resulting in the formation of lipoma ^[1]. A study by Khadilkar et al. differentiated lipomas from pseudo-lipomas through the existence of a fibrous capsule ^[9]. The swelling in this present case was able to be identified as a lipoma through the existence of a thin fibrous capsule with a progressive enlargement in size. Dholakia and colleagues reported of the five regions in the foot and ankle, namely, the ankle, heel, dorsum of the foot, plantar surface of the foot, and toes for showing the site of the tumor ^[11] which is consistent with our findings where the lipoma extended from the medial arch of the foot to the base of the second toe. Although clinically a convincing diagnosis is made, tumors with uncharacteristic clinical features might require radiological examination such as ultrasound, computerized tomography (CT) scan, or magnetic resonance imaging (MRI) which is standard for investigating soft-tissue tumors [3, 8]. Septa below 2 mm on CT and MRI imaging are suggestive features of lipoma ^[11]; however, these investigations are not routinely done in our subregion mainly due to cost and availability. Ultrasound is mostly the preferred imaging technique which is why it was requested for this patient the case report. Lipoma of the foot must be distinguished from other lipomata lesions like fat herniation. Lipomas are different from herniation of adipose tissue as the latter will not increase in size or be encaged by fibrous capsules. Liposarcoma, Kaposi sarcoma, or synovial sarcoma are malignant soft tissue sarcoma of the foot that is to be differentiated from lipoma ^[15]. Excision biopsy is the current treatment that gives a definite diagnosis as was done in this case report ^[3].

Soft-tissue swelling of the lower extremity especially of the foot is uncommon with an asymptomatic presentation. Findings of Doppler ultrasound suggested a diagnosis of hematoma, this diagnosis was found to be a lipoma during the excision biopsy which was later confirmed by histopathological examination of the excised mass. Therefore, lipoma should be a differential diagnosis of a swelling on the sole of the feet associated with trauma as in the case presented. This case is of significance because the ultrasound diagnosis was a hematoma which was false and led to mismanagement of the patient until the correct diagnosis was made intraoperatively. Furthermore, a lipoma is mostly painless but became painful on trauma to the surrounding tissues; hence, it became a case of scientific importance. With the correct diagnosis and treatment made, the patient was able to return to full activity after 6 months of treatment and follow-up and she was grateful to our team.

Soft tissue swelling of the lower extremity especially on the sole foot is uncommon with an asymptomatic presentation like this case. However, a detailed clinical evaluation will always help the clinician have a high index of suspicion for a rather rare location of a common condition like this case despite a contrary sonographic finding. Therefore, a lipoma should be a differential diagnosis of a swelling on the sole of the feet associated with trauma as in the case presented.