> Table of Contents > Lipoma
Lipoma
Bradley M. Turner, MD, MPH, MHA
image BASICS
DESCRIPTION
  • Lipomas are the most common soft tissue tumor (benign or malignant).
  • One of several distinct benign lipomatous tumors. In its most conventional (simple) form, lipomas are composed of mature adipose tissue, typically enveloped by a well-defined thin fibrous capsule.
  • Not distinguishable histologically from normal adipose tissue
  • Several nonconventional forms of lipomas (less commonly encountered) have been described, which may present in multiple locations, contain varying amounts of both adipose and nonadipose tissue, and/or have more atypical cytologic features.
  • These nonconventional variants include chondroid lipoma, myolipoma, lipoblastoma, angiolipoma, spindle cell lipoma/pleomorphic lipoma, intramuscular/intermuscular lipoma, lipoma of tendon sheath and joint, lipoma arborescens, lipomatosis of nerve, diffuse lipomatosis, multiple symmetric lipomatosis, adiposis dolorosa, and hibernoma.
  • Typically slow growing, superficial (subcutaneous), and asymptomatic; less commonly presents as a painful (angiolipoma) or deep-seated lesion
  • May present as an infiltrative lesion (cellular angiolipoma, diffuse lipomatosis, multiple symmetric lipomatosis (Madelung disease), and adiposis dolorosa (Dercum disease)
  • Often found in the upper trunk, especially the shoulders, back, neck, and head; but can be found anywhere in the body
  • Lipomas have been reported in anatomic locations as varied as cardiac, intrathoracic, endobronchial, retroperitoneal, breast, calf, thigh, scapular, intraosseous, fingers, palmar, toe, epidural, spinal, intra-articular (knee), parapharyngeal, nasopharyngeal, adrenal, inguinal, bladder, scrotal, ovarian, intracranial, intraneural, and GI tract (most often in the ileum).
  • Lipomas can cause respiratory distress due to bronchial obstruction of major airways, GI obstruction or bleeding, neuropathic symptoms from compression in locations such as the forearm or ankle, or cord compression if in dural/medullary components of the spinal cord.
  • Must be differentiated from other tumors, particularly liposarcomas, as treatment protocols differ.
EPIDEMIOLOGY
  • Lipomas can occur at any age but most commonly occur in middle-aged adults, typically in the 40- to 60-year-old age group.
  • Hibernomas typically present in the 3rd decade.
  • Conventional lipomas and most variants are rare in children; however, lipoblastoma and diffuse lipomatosis typically present in children <3 years of age.
  • No clear gender predilection in conventional lipomas and most variants.
  • Females reportedly more commonly diagnosed with chondroid lipoma, myolipoma, and adiposis dolorosa.
  • Males reportedly more commonly diagnosed with spindle cell/pleomorphic lipoma, intramuscular/intermuscular lipoma, lipoblastoma, and multiple symmetric lipomatosis.
  • Approximately 5% of patients have multiple lipomas.
Incidence
Has been reported as 2.1 per 1,000 individuals per year; however, incidence is difficult to accurately estimate.
Prevalence
Has been reported as present in ˜1% the population; however, as with incidence, prevalence is difficult to accurately estimate and is most likely underestimated.
ETIOLOGY AND PATHOPHYSIOLOGY
  • The etiology and pathogenesis of lipomas is unclear.
  • A pathogenetic link between soft tissue trauma and the formation of lipomas has been suggested.
  • Two potential explanations to correlate soft tissue trauma and adipose tissue tumor growth have been proposed:
    • Formation of so-called posttraumatic pseudolipomas by prolapsing adipose tissue through fascia resulting from direct impact
    • Lipoma formation as a result of preadipocyte differentiation and proliferation mediated by cytokine release following soft tissue trauma and hematoma formation
Genetics
  • Approximately 2/3 of lipomas demonstrate chromosomal aberrations.
  • The most common chromosomal aberrations are rearrangements of the chromatin remodeling gene HMGA2 on chromosome 12q15 (67%).
  • Less common chromosomal aberrations include anomalies of the 13q12-22 region (15%) and rearrangements of the 6p21 region (5%).
  • Frequent association of chromosomal aberrations in the long arm of chromosomes 13 and 16 with spindle cell/pleomorphic lipomas
  • Consistent chromosomal aberrations identified in the long arm of chromosome 11 with hibernomas
  • Various case reports of other chromosomal aberrations exist.
RISK FACTORS
  • Because the pathogenesis of lipomas is unclear, risk factors are difficult to qualify.
  • Possible risk factors include obesity, alcohol abuse, liver disease, glucose intolerance, and soft tissue trauma (see “Etiology and Pathophysiology”).
COMMONLY ASSOCIATED CONDITIONS
May appear as part of a hereditary syndrome: Dercum disease, Madelung syndrome (also known as Launois-Bensaude syndrome), Gardner syndrome, Cowden syndrome, and Bannayan-Riley-Ruvalcaba syndrome (children)
image DIAGNOSIS
PHYSICAL EXAM
  • Lipomas are usually soft, homogenous, oval, and nontender, with a rubbery or doughy consistency; if hard, suspect another diagnosis.
  • The overlying skin is typically mobile and normal in appearance; if erythematous, suspect another diagnosis such as infection.
  • Lipomas are commonly ≤5 cm in diameter. If larger, this raises suspicion for liposarcoma (1), although lipomas can be >10 cm (2,3).
DIFFERENTIAL DIAGNOSIS
  • Differential diagnosis includes a variety of benign and malignant tumors (1,4).
  • The most common considerations include epidermal inclusion cyst, trichilemmal cysts, hematoma, vasculitis, panniculitis, rheumatic nodules, abscess/infection, and malignant disease.
  • Trichilemmal cysts can often be differentiated from lipomas by their characteristic central punctum and surrounding induration.
  • An abscess typically has pain, along with overlying induration and erythema.
  • Diagnosis may be more challenging with other lesions, particularly deeper-seated lesions.
  • Imaging, core needle biopsy, or excision can be useful in further clarifying the diagnosis (1,2,3,4).
DIAGNOSTIC TESTS & INTERPRETATION
Patients presenting with smaller (≤5 cm) subcutaneous lesions that are clinically considered lipomas typically will not receive preoperative imaging. Larger lesions with irregular shape and/or suggestion of myofascial involvement should receive preoperative imaging (1)[A].
Initial Tests (lab, imaging)
  • Because of differences in treatment, prognosis, and long-term follow-up, it is important to preoperatively distinguish lipomas from liposarcomas and other malignant lesions (2,3,4,5,6). If there is doubt regarding nature of the lipoma, further testing is indicated.
  • US, MRI, or CT can be used in the suspected diagnosis of lipoma (1,2).
  • US may be limited with larger lesions or lesions which have atypical patterns (2).
  • MRI is the most sensitive imaging modality for lipomatous masses, has a high negative predictive value (1)[A], and can be useful when US is equivocal (2)[A].
  • MRI can be extremely helpful in distinguishing a lipoma from a liposarcoma (1,2)[B], although lipoma variants may show characteristics of a liposarcoma due to the presence of decreased adipose tissue, nonadipose tissue, and/or irregular margins.
  • MRI findings suggestive of liposarcoma include nonadipose areas, a partially ill-defined margin, neurovascular involvement, enhancing thick/nodular septum, a bright signal intensity on T1-weighted images that are not completely suppressed on T1 fat suppression images, and a high T2 signal within the lesion (1,2,3).
Diagnostic Procedures/Other
  • If diagnosis is in doubt, an open surgical incisional biopsy has traditionally been considered the “gold standard” to obtain a histologic diagnosis (4).
  • A core-needle biopsy has been proposed as a preferred biopsy method that can provide accurate diagnosis and assessment of malignant potential if examined by an experienced pathologist (4)[C].
  • Fine needle aspiration cytology is not considered appropriate for the initial diagnostic evaluation of mesenchymal tumors (4).
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Test Interpretation
  • Pathologic interpretation is still generally considered as the “gold standard” of diagnosis (1,4).
  • Lipomas are typically composed of benign adipose tissue, with inconspicuous nuclei, and varying amounts of connective tissue.
  • Lipomas are typically surrounded by a fibrous, welldefined thin capsule that is separate from the surrounding tissue; however, this may not be present on the microscopic tissue due to sampling bias.
  • Atypical features such as prominent or atypical nuclei, inflammation, fibrosis, and necrosis may be present and may be mistaken for atypical features seen in atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) (5).
  • Pathologists may overcall a diagnosis of ALT/WDL in lipomas with atypical features (1,5,6).
  • Complementary molecular testing may augment histologic diagnosis in challenging cases, as MDM2 gene amplification is not present in benign lipomas but has been reported to be a highly sensitive marker in ALT/WDL (3,5,6)[B].
image TREATMENT
  • If diagnostically certain that the lesion is a benign lipoma, observation is a consideration.
  • Treatment of lipoma typically consists of surgical excision; however, advances in medical treatment can shrink lipomas (1)[A].
  • Treatments like steroid injection or liposuction can be cosmetically useful in superficial lesions, particularly in locations where scars should be avoided (1)[A], although liposuction has not always been associated with the best aesthetic outcomes (1)[C].
  • A successful trial of lipomas treated with subcutaneous deoxycholate injections has been reported, suggesting that low-concentration deoxycholate may be a relatively safe and effective treatment for small collections of adipose tissue (1)[C].
  • Indications for removal of a suspected lipoma include diagnostic uncertainty, cosmetic concerns, nerve impingement, pain, increase in size, irregular characteristics, size >5 cm, samples of a core needle biopsy consistent with atypical features, or features consistent with a sarcoma (1)[A].
SURGERY/OTHER PROCEDURES
  • Surgical removal techniques include enucleation/excisional biopsy and open incisional biopsy (1,4).
  • In uncomplicated cases, the excision can be performed in the office or in the minor procedure room under local anesthetic.
  • Plan the incision to follow skin lines, if possible, to minimize scarring. Use a surgical marker to draw out the palpable margins of the lipoma and the planned incision. The incision should be ˜50-75% of the length of the lipoma along Langer lines (defined as parallel skin creases correlating with the direction of least elasticity) (1)[C].
  • After anesthetizing the skin with a local anesthetic, a linear incision is carried out down to the level of the capsule using a number 11 or 15 blade.
  • Blunt dissection (curved hemostat) and sharp dissection (iris scissor) are used to separate the fibrous capsule from the surrounding soft tissue. Care must be taken not to invade the capsule to maintain proper aesthetics (1).
  • As the lobule is lifted, the dissection is continued to free up the entire tumor.
  • Apply pressure to the outside of the lipoma to express it through the skin opening. In many cases, the lipoma will simply pop out. If not, more dissection may be needed, or the incision may need to be lengthened.
  • After the lipoma is out, pressure with gauze is usually all that is needed to obtain good hemostasis. If bleeding persists, use electrocoagulation before closing the incision (1).
  • If necessary, dead space may be closed with deep absorbable sutures. The skin may be closed with nonabsorbable simple interrupted sutures or skin adhesive.
  • A minimal scar technique to facilitate removal from a small incision using segmental dissection of the lipoma has been described (1)[B].
  • It is advisable to send all biopsied tissue to pathology (1)[C].
image ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Usual surgical follow-up is needed to monitor for any complications.
PATIENT EDUCATION
Handout: “What are lipomas?” Am Fam Physician. 2002;65(5):905. Available at: http://www.aafp.org/afp/20020301/905ph.html
PROGNOSIS
Most lipomas grow very slowly, are asymptomatic, and remain stable. Recurrence after excision is rare (1-2%), unless the excision was incomplete.
REFERENCES
1. Pandya KA, Radke F. Benign skin lesions: lipomas, epidermal inclusion cysts, muscle and nerve biopsies. Surg Clin North Am. 2009;89(3):677-687.
2. Strauss DC, Qureshi YA, Hayes AJ, et al. The role of core needle biopsy in the diagnosis of suspected soft tissue tumours. J Surg Oncol. 2010;102(5):523-529.
3. Jaovisidha S, Suvikapakornkul Y, Woratanarat P, et al. MR imaging of fat-containing tumours: the distinction between lipoma and liposarcoma. Singapore Med J. 2010;51(5):418-423.
4. Brisson M, Kashima T, Delaney D, et al. MRI characteristics of lipoma and atypical lipomatous tumor/well-differentiated liposarcoma: retrospective comparison with histology and MDM2 gene amplification. Skeletal Radiol. 2013;42(5):635-647.
5. Zhang H, Erickson-Johnson M, Wang X, et al. Molecular testing for lipomatous tumors: critical analysis and test recommendations based on the analysis of 405 extremity-based tumors. Am J Surg Pathol. 2010;34(9):1304-1311.
6. Weaver J, Downs-Kelly E, Goldblum JR, et al. Fluorescence in situ hybridization for MDM2 gene amplification as a diagnostic tool in lipomatous neoplasms. Mod Pathol. 2008;21(8):943-949.
Additional Reading
&NA;
  • Aust MC, Spies M, Kall S, et al. Posttraumatic lipoma: fact or fiction? Skinmed. 2007;6(6):266-270.
  • Bancroft LW, Kransdorf MJ, Peterson JJ, et al. Benign fatty tumors: classification, clinical course, imaging appearance, and treatment. Skeletal Radiol. 2006;35(10):719-733.
  • Gaskin CM, Helms CA. Lipomas, lipoma variants, and well-differentiated liposarcomas (atypical lipomas): results of MRI evaluations of 126 consecutive fatty masses. AJR Am J Roentgenol. 2004;182(3):733-739.
  • Liang CW, Mariño-Enríquez A, Johannessen C, et al. Translocation (Y;12) in lipoma. Cancer Genetics. 2011;204(1):53-56.
  • Macchia G, Nord KH, D'Alessandro G, et al. Rearrangements of chromosome bands 15q12-q21 are secondary to HMGA2 deregulation in conventional lipoma. Oncol Rep. 2014;31(2):807-811.
  • Rotunda AM, Ablon G, Kolodney MS. Lipomas treated with subcutaneous deoxycholate injections. J Am Acad Dermatol. 2005;53(6):973-978.
  • Salam GA. Lipoma excision. Am Fam Physician. 2002;65(5):901-904.
Codes
&NA;
ICD10
  • D17.9 Benign lipomatous neoplasm, unspecified
  • D17.79 Benign lipomatous neoplasm of other sites
  • D17.1 Benign lipomatous neoplasm of skin, subcu of trunk
Clinical Pearls
&NA;
  • Lipomas are slow growing, often asymptomatic, and typically diagnosed without imaging or biopsy.
  • Asymptomatic subcutaneous lipomas can be followed clinically unless there is diagnostic uncertainty, they are causing cosmetic or pain problems, are large (>5 cm) or growing rapidly, or causing compression of vital organs/nerves.
  • Most symptomatic lipomas are removed surgically. With the appropriate indications, nonsurgical options are available.
  • In uncomplicated cases, excision can be performed in the office setting and do not require preoperative testing.
  • Consider referral to a subspecialist if a lipoma is in a delicate anatomic location or if there is a concern that the lesion might be malignant.