Lipoma
A lipoma is a benign (non-cancerous) growth made up of mature fat cells. Lipomas are very common and can appear anywhere in the body where fat is present, including the limbs, trunk, neck, and soft tissues. They typically grow slowly, feel soft or rubbery, and are usually painless. Most are discovered incidentally or because a person notices a soft lump under the skin.
What is it?
A lipoma is a benign tumor composed of normal fat cells surrounded by a thin capsule. Although called a “tumor,” lipomas are not cancerous and do not turn into cancer. They can occur anywhere in the soft tissues of the body and often remain stable in size for years. Some may become noticeable if they enlarge or occur in a visible location.
On imaging, lipomas have characteristic features that allow radiologists to distinguish them from other soft tissue masses. MRI, in particular, shows a uniform fatty appearance that confirms the diagnosis. Lipomas inside deeper tissues or near muscles may be evaluated with imaging to ensure they are benign.
Important to Know
Most lipomas do not cause symptoms and do not require treatment. However, they can occasionally grow large enough to cause discomfort, limit movement, or compress nerves. Lipomas that grow rapidly, become painful, or develop atypical features on imaging may require further evaluation to rule out rare tumors such as liposarcoma.
Red flags include sudden enlargement, persistent pain, firmness, or changes in the overlying skin. Surgical removal may be recommended if the lipoma is symptomatic or cosmetically concerning. Follow-up imaging is usually not necessary unless there are atypical features or continued growth.