Lipoma is a benign tumor that arise from mature fat cells. It’s probably the most common benign tumors of connective tissue.

  • It can be found at any age and in either sex but are probably more common in middle-aged women (20-40 years).
  • Lipomas are multifocal, and in rare instances they are symmetrical.
  • Multiple lesions will be found in 5-10% of patients with a known superficial lipoma.

Dercum’s disease is a rare disorder characterized by multiple, painful lesions.

Location

  • It can occur in a subcutaneous, intramuscular, or intermuscular location.
  • Occasionally affects the synovium (arborescens) and rarely the periosteum.
  • Superficial lesions are common in the upper back, thighs, buttocks, shoulders and arms
  • Deep lesions are affixed to surrounding muscle, in the thighs, shoulders and arms
See Also: Differential Diagnosis for Bone Lesions

Types of Lipoma

Spindle cell lipoma

  • Spindle cell lipoma commonly occurs in men (45-65 years of age).
  • Clinically: manifests as a solitary, painless, growing, firm nodule.
  • Histology: mixture of mature fat cells and spindle cells. There is a mucoid matrix with a varying number of birefringent collagen fibers.
  • Treatment: excision with a marginal margin.

Pleomorphic lipoma

  • Pleomorphic lipoma occurs in middle-aged patients.
  • Clinically: Manifests as a slow-growing mass
  • Histology: characterized by lipocytes, spindle cells, and scattered bizarre giant cells
  • Treatment: excision with a marginal margin.
  • This lesion may be confused with different types of liposarcoma.

Angiolipoma

  • Angiolipoma is the only lipoma that is very painful when palpated.
  • Clinically: Manifests with small nodules in the upper extremity that are intensely painful.
  • MRI: may show a small fatty nodule or completely normal appearance.
  • Histology: Angiolipoma consists of mature fat cells (as in a typical lipoma) and nests of small arborizing vessels.

Angiomyolipoma

  • Angiomyolipoma is usually found in the kidney.
  • Histology: It is composed of smooth muscle, blood vessels, and fat.
  • This tumor occasionally is associated with changes of tuberous sclerosis in the brain.

Hibernoma

  • Hibernoma also known as fetal fat cell lipoma.
  • Histology: It is composed of large, finely vacuolated foam cells, is lobulated, and simulates the hibernating organs of some animals.
  • It has a distinctive brown appearance and may become quite large.

Lipoblastomatosis

  • Lipoblastomatosis consists of embryonal fat and occurs more often in infants and young children.
  • This tumor resembles some types of liposarcoma but has a distinct lobular pattern and no atypical nuclei.

Clinical Evaluation

  • The Lipomas are soft, circumscribed, movable masses that are painless (except angiolipoma) and slow growing.
  • A knee effusion is characteristically the presenting complaint in patients with arborescens type.

Radiographic Evaluation

  • On plain radiograph, large masses appear as discrete radiolucent areas within soft tissue.
  • MRI usually provides a definitive diagnosis because the lesions are uniformly bright on T1-weighted images and are dark on fat-suppressed sequences like the surrounding subcutaneous tissue.

Mineralization of the lesion on plain radiograph should raise suspicious for synovial cell sarcoma.

Histology

  • Biopsy often not necessary.
  • Mature fat cells with flattened nuclei, and mitotic activity is absent.

Treatment

Non-operative

  • Benign lesions that are painless can be treated by observation only.

Operative

  • Operative treatment is indicated if the mass is growing or causing symptoms.
  • Surgical treatment consists of excision with a marginal line of resection or an intralesional margin.
  • Local recurrence is uncommon.