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

Radiographs may show a radiolucent lesion in the soft tissues if the lipoma is deep within the muscle or
between muscle and bone.

CT scan or MRI shows a well-demarcated lesion with the same signal characteristics as those of mature fatbon all sequences. On fat suppression sequences, the lipoma has a uniformly low signal.

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.

Differential Diagnosis

Differential is liposarcoma

LIPOMALIPOSARCOMADEDIFFERENTIATED LIPOSARCOMA
HistorySlowly enlarging mass May be incidentally foundSlowly enlarging mass
May be incidentally found
Mass that has been present begins to grow
Enlarging mass
Pain
ImagingConsistent with fat on all imagingConsistent with fat on all imaging
May have areas of heterogeneity
Areas consistent with fat and other areas appear similar to soft tissue sarcoma
PathologyFatFat, Immature lipoblasts
MDM2 (+)
Fat juxtaposed to high grade elements
Treatmentlipoma removal + Marginal excisionMarginal excision +/− radiationWide excision and radiation

Treatment

Non-operative

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

If the patient experiences no symptoms and the radiographic features are diagnostic of lipoma, no treatment is necessary

Operative

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