A lipoma is a common, non-cancerous growth composed of mature fat cells, making it the most frequent type of soft tissue tumor found in adults. This benign mass typically develops just beneath the skin, presenting as a soft, rubbery lump that is easily movable when touched. While most lipomas appear spontaneously in individuals without any clear cause, the presence of multiple lipomas often raises the question of a hereditary link. The development of these fatty tumors is complex, involving both genetic predisposition and non-inherited risk factors.
What Exactly Is a Lipoma?
A lipoma is an overgrowth of adipose tissue, the body’s primary fat storage material. These tumors are well-defined and usually enclosed by a thin, fibrous capsule. They are found most often in the subcutaneous layer, commonly appearing on the neck, shoulders, back, abdomen, and limbs.
The typical lipoma is slow-growing and generally measures less than five centimeters in diameter. A defining feature is their soft, doughy texture and the ability to be pushed around freely under the skin without causing pain. Most lipomas do not require intervention unless they become symptomatic, grow rapidly, or cause cosmetic concern.
When Lipomas Are Inherited
While a single lipoma is usually a sporadic event, the development of multiple lipomas is strongly associated with inherited conditions called lipomatoses. The most recognized is Familial Multiple Lipomatosis (FML), characterized by the progressive appearance of numerous encapsulated lipomas across the trunk and extremities. This rare condition follows an autosomal dominant inheritance pattern, meaning a person only needs to inherit one copy of the altered gene from a single parent to develop the disorder.
Genetic studies have implicated several genes in familial lipomatosis, including the HMGA2 gene located on chromosome 12. Rearrangements in this gene are frequently observed, suggesting the gene’s function is disrupted, leading to the uncontrolled proliferation of fat cells. Other inherited conditions also feature lipomas, such as Cowden syndrome and Gardner syndrome, which are linked to mutations in tumor suppressor genes like PTEN. These broader syndromes demonstrate that hereditary lipomas are often a physical manifestation of an underlying systemic genetic issue.
Other Factors Contributing to Lipoma Development
The majority of lipoma cases are sporadic, meaning they occur without a clear family history or genetic syndrome. Age represents a significant risk factor, as lipomas are most commonly diagnosed in adults between 40 and 60 years old. The exact mechanism for their development in these sporadic cases remains unclear, but they are thought to arise from localized changes in fat cell regulation.
General health factors, such as obesity and underlying metabolic disorders, also contribute to the likelihood of developing lipomas. A theory suggests that some lipomas, known as post-traumatic lipomas, may be triggered by a localized blunt injury. Trauma may cause inflammation or fat cell rupture, initiating a cascade that leads to the formation of the fatty tumor at the injury site.
Confirming Diagnosis and Treatment Options
The initial diagnosis of a lipoma is typically made through a physical examination, where a physician assesses the soft, movable, and non-tender nature of the lump. Imaging studies confirm the composition of the mass and rule out other possibilities, such as a fluid-filled cyst or a malignant tumor like a liposarcoma. An ultrasound shows the fatty, homogeneous nature of the growth, while magnetic resonance imaging (MRI) provides a detailed view for larger or deeper lesions.
If the diagnosis remains uncertain or if the lipoma exhibits rapid growth, unusual firmness, or pain, a biopsy may be performed to analyze a small tissue sample. Since most lipomas are harmless, management often involves simple observation if the mass is small and asymptomatic. For lipomas that are large, symptomatic, or cosmetically bothersome, the primary treatment is surgical excision. This involves removing the entire fatty mass and its surrounding capsule to minimize the chance of recurrence. An alternative, less invasive option for smaller lipomas is liposuction, which uses a needle and a large syringe to extract the fatty tissue.