Lipoma overview

# Overview
A lipoma is a common, benign tumor composed of fatty tissue. In 1914, Dr. Gery and colleagues first described Hibernoma, tumor of brown fat tissue. Lipoma may be classified into different subtypes depending on the classification system. They may be classified according to the anatomical location, the related tissues or other characteristics. Lipoma is formed from mature adipocytes and is histologically indistinguishable from fat tissue. Recent studies have observed cytogenetic abnormalities in 50-60% of lipomas, suggesting its role in the lipoma pathogenesis. Rearrangements of chromosome 12 are the most commonly cytogenetic abnormality. In a cross-sectional appearance, the lipoma is pale yellow to orange color and has a uniform greasy surface with a lobular pattern. The subcutaneous lipoma is usually encapsulated and has a distinct lobulated pattern. There is no established cause for lipoma. However, trauma and some genetic abnormalities have been associated with its development. Lipoma must be differentiated from liposarcoma, normal adipose tissue, adrenal myelolipoma, angiomyolipoma, and other lipomatous tumors. Lipoma incidence is 100 per 100,000 individuals worldwide annually. Lipomas tend to affect middle age individuals. It affects men at a greater extent than women. Common risk factors in the development of lipoma are trauma and genetic factors. Lipoma affects trunk, shoulder, upper arm, and neck at a greater extent. These tumors are completely benign and recurrence is one of their complications. Lipoma can be diagnosed clinically. However, a combination of clinical features and imaging studies are usually used for their diagnosis. Biopsy may be indicated in case of rapidly enlarging mass or unusual findings such as firm consistency. The most common symptom of lipoma is an asymptomatic slowly growing mass with a soft consistency. However, the deep lipoma may be symptomatic depending on their site and size. Symptoms include pain, restriction of movement in large lipoma, feeling of fullness or discomfort, and  palpitation and dyspnea in mediastinal lipomas. Physical examination of patients with a lipoma is usually remarkable for a mobile, painless mass with a soft consistency. This mass often occurs in the neck, shoulders, back, arms and thighs. Sometimes, lipoma may cause limitation in the range of motions of the extremities depending on their size and locations. Neuromuscular examination of patients with lipoma may be remarkable for positive Tinel's sign and Phalen's sign. Lasegue's sign may be positive in case of lumbosacral lipoma. On CT, the lipoma is seen as a well-delineated mass with absorption density characteristic of fatty tissue. Findings on an MRI suggestive of lipoma include a well-defined lesion with intensity similar to that of subcutaneous fat. Ultrasound may be helpful in the diagnosis of lipoma. Findings on an ultrasound suggestive of lipoma include Hypoechoic, minimally heterogeneous lesion. Treatment options of lipoma include simple excision, liposuction, and deoxycholate injection.

# Historical Perspective
In 1914, Dr. Gery and colleagues first described Hibernoma, tumor of brown fat tissue.

# Classification
Lipoma may be classified into different subtypes depending on the classification system. They may be classified according to the anatomical location, the related tissues or other characteristics.

# Pathophysiology
Lipoma is formed from mature adipocytes and is histologically indistinguishable from fat tissue. Recent studies have observed cytogenetic abnormalities in 50-60% of lipomas, suggesting its role in the lipoma pathogenesis. Rearrangements of chromosome 12 are the most commonly cytogenetic abnormality. In a cross-sectional appearance, the lipoma is pale yellow to orange and has a uniform greasy surface with a lobular pattern. The subcutaneous lipoma is usually encapsulated and has a distinct lobulated pattern.

# Causes
There is no established cause for lipoma. However, trauma and some genetic abnormalities have been associated with its development.

# Differentiating Lipoma other Diseases
Lipoma must be differentiated from liposarcoma, normal adipose tissue, adrenal myelolipoma, angiomyolipoma, and other lipomatous tumors.

# Epidemiology and Demographics
Lipoma incidence is 100 per 100,000 individuals worldwide annually. Lipoma tend to affect middle age individuals, especially those of 40 to 60 years of age. It affects men at a greater extent than women.

# Risk Factors
Common risk factors in the development of lipoma are trauma and genetic factors.

# Screening
There is insufficent evidence to recommend routine screening for lipoma.

# Natural History, Complications and Prognosis
Lipoma tends to affect individuals of 40 to 60 years of age. It affects trunk, shoulder, upper arm, and neck at a greater extent. They are completely benign and recurrence is one of their complications.

# Diagnosis
Lipoma can be diagnosed clinically. However, a combination of clinical features and imaging studies are usually used for the diagnosis of lipoma. Biopsy may be indicated in case of rapidly enlarging mass or unusual findings such as firm consistency.

## History and Symptoms
The most common symptom of lipoma is an asymptomatic slowly growing mass with a soft consistency. However, the deep lipoma may be symptomatic depending on their site and size. Symptoms include pain, restriction of movement in large lipoma, feeling of fullness or discomfort, and  palpitation and dyspnea in mediastinal lipomas.

## Physical Examination
Physical examination of patients with a lipoma is usually remarkable for a mobile, painless mass with a soft consistency. This mass often occur in the neck, shoulders, back, arms and thighs. Sometimes, lipoma may cause limitation in the range of motions of the extremities depending on their size and locations. Neuromuscular examination of patients with lipoma may be remarkable for positive Tinel's sign and Phalen's sign. Lasegue's sign may be positive in case of lumbosacral lipoma.

## Laboratory Findings
There are no diagnostic laboratory findings associated with lipoma.

## Electrocardiogram
There is no electrocardiogram finding associated with lipoma.

## X Ray
There are no x-ray findings associated with lipoma. however, it may have findings suggestive of the presence of a mass.

## CT
On CT, the lipoma is seen as a well-delineated mass with absorption density characteristic of fatty tissue.

## MRI
MRI may be helpful in the diagnosis of lipoma. Findings on an MRI suggestive of lipoma include a well-defined lesion with intensity similar to that of subcutaneous fat.

## Echocardiography or Ultrasound
Ultrasound may be helpful in the diagnosis of lipoma. Findings on an ultrasound suggestive of lipoma include Hypo-echoic, minimally heterogeneous lesion.

## Other Imaging Findings
There are no other imaging findings associated with lipoma.

## Other Diagnostic Studies
Other diagnostic studies for lipoma include biopsy, which demonstrates mature fat cells with no malignant feature.

# Treatment

## Surgery
Surgery of lipoma includes simple excision, liposuction, and deoxycholate injection.

## Primary Prevention
There are no established measures for the primary prevention of lipoma.

## Secondary Prevention
There are no established measures for the secondary prevention of lipoma.