Rapidly growing soft-tissue mass on the left thigh

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Eosinophilia along with size and growth rate of the mass could have derailed this patient’s diagnosis.

Mr. M, a 56-year-old from Africa, presented with a fast-growing soft mass over the left thigh. He first noticed the mass two years ago and reported rapid growth over the past year. He denied pain or other soft-tissue changes. His medical history was positive for tobacco use and malaria that was resolved. His surgical history was unremarkable.

PHYSICAL EXAMINATION

The patient’s vital signs, including temperature, were within normal limits. On examination, a soft, mobile, nontender, and well-circumscribed soft-tissue mass measuring 18 x 15 x 8 cm was visible over his left thigh (Figure 1). A WBC count with differential revealed a higher-than-usual percentage of eosinophils (7.8%). Because the size of the mass raised suspicions of malignancy and the mass was causing the patient discomfort, we opted to remove it. Surgical resection yielded a lobulated soft-tissue mass weighing 384 g and measuring 11.5 x 12 x 6 cm.

POSSIBLE DIAGNOSES

The differential diagnoses for soft-tissue pathologies are many and include liposarcoma, lipoma, epidermal cyst, dermoid cyst, rhabdomyoma, infection, and infiltrative disease (Table 1). Liposarcoma is a slow-growing malignant tumor composed of fatty tissue, while a lipoma is a benign soft-tissue tumor.

Epidermal cysts, also called sebaceous cysts or epidermoid cysts, are subcutaneous closed sacs filled with sebum. Present at birth, dermoid cysts are saclike growths that can contain fluid or structures found on or in the skin, such as hair, teeth, or glands. Rhabdomyomas are benign striated-muscle tumors that mainly affect the head and neck; in rare cases, they can also affect cardiac muscle.

Soft-tissue masses may also signal infection, such as nodular fasciitis, onchocerciasis, and loiasis. Kimura disease presents as large subcutaneous masses on the head or neck of East Asian males, while angiolymphoid hyperplasia with eosinophilia occurs in all races and is characterized by smaller and more superficial lesions. Both Kimura disease and angiolymphoid hyperplasia feature eosinophilia and are of unknown origin.1

Other possibilities are hematoma, fibroma, giant cell tumor of soft tissues, hemangioma, soft-tissue chondroma, neuroma, rheumatic nodules, erythema nodosum, and metastatic tumors. Based on the fast-growing nature of the mass and the presence of eosinophilia, sarcoma seemed the most likely diagnosis. However, given Mr. M’s place of origin, I could not rule out parasitic infection, such as onchocerciasis or loiasis. Other less likely possibilities were mastocytosis, eosinophilic panniculitis, and Kimura disease.

Microscopic examination of the resected tumor revealed mature adipose tissue with no cellular atypia, confirming the diagnosis of lipoma. The eosinophilia, which is not commonly seen with lipoma, improved upon resection.

ANALYSIS

Lipomas are benign, mostly asymptomatic, slow-growing fatty-tissue tumors. Found primarily in the subcutaneous tissue,2 lipomas also develop in deep tissues, such as muscles, and in the thoracic, abdominal, pelvic, and cranial cavities.3,4 The tumors can be diagnosed by clinical examination. Radiologic studies may facilitate the diagnosis; histology is confirmatory.2

Three findings set our patient’s tumor apart from a typical lipoma: size, rate of growth, and presence of eosinophilia. Most lipomas remain small (<5 cm in diameter) over the years, although in rare cases, they can grow large. Eosinophilia is not generally seen in patients with lipoma.

Lipomas usually do not require treatment. However, if the lipoma is in a bothersome location, painful, or growing, it can be resected, as it was in our patient’s case.

Dr. Skeik is instructor of medicine, Dartmouth Medical School in Hanover, N.H., assistant professor of medicine at the University of Southern Maine in Portland, and an internist at St. Mary’s Regional Medical Center in Lewiston, Maine. Dr. Jabr is an internist with Health Associates of Peace Harbor in Florence, Ore.

References

1. Chen H, Thompson LD, Aguilera NS, Abbondanzo SL. Kimura disease: a clinicopathologic study of 21 cases. Am J Surg Pathol. 2004;28:505-513.

2. Samper A, Ruiz de Erenchun R, Yeste L, Bazan A. Dermoid cyst on the auriculotemporal area. Plast Reconstr Surg. 2000;106:947-948.

3. Bigelow DC, Eisen MD, Smith PG, et al. Lipomas of the internal auditory canal and cerebellopontine angle. Laryngoscope. 1998;108:1459-1469.

4. Zimmermann M, Kellermann S, Gerlach R, Seifert V. Cerebellopontine angle lipoma: case report and review of the literature. Acta Neurochir (Wien). 1999;141:1347-1351.

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