Intramuscular lipoma is a benign subcutaneous mesenchymal neoplasm composed of fatty cells that arises within the muscle. It is usually solitary but may be present within multiple muscles. It is a benign condition that rarely co-occurs with other types of tumors. Intramuscular lipomas are a rare lipoma subtype (less than 1% of lipomas are intramuscular); the majority of intramuscular lipomas are infiltrative (as opposed to defined).

Intramuscular lipoma can present at any age, but they are most common in patients aged 40-70. Intramuscular lipomas most often present in the thigh, upper limb, shoulder, and chest wall; however, they have been found in the trunk, neck, head, lower limb, cheek, and tongue.

Intramuscular lipomas are characterized by soft, palpable, usually painless masses that grow slowly, often over months to years. While commonly asymptomatic, lesions can cause pain (although this is a late finding) and, uncommonly, impairment in muscle function. Other signs and symptoms depend on the location of the intramuscular lipoma:

• Tongue – trouble with mastication, speech, and deglutition
• Deltoid region – reduced motion, superficial venous congestion
• Pectoralis muscle – signs resemble those of breast cancer
• Supraspinatus muscle – signs resemble those of impingement syndrome
• Chest wall – signs resemble those of a pulmonary nodule
• Retropharyngeal space – dysphagia and dysphonia
• Superior oblique muscle – diplopia and proptosis

In deep-seated lipomas, care must be taken to rule out malignancy with MRI and biopsy.