A lipoma is the most common tumor present in the body. It is also the most common benign tumor in the body. It is composed of fat cells of adult type. It can occur anywhere in the body, that is why it is often called ‘universal tumor’ or ‘ubiquitous tumor’.
A lipoma is the most common tumor present in the body. It is also the most common benign tumor in the body. It is composed of fat cells of adult type. It can occur anywhere in the body, that is why it is often called ‘universal tumor’ or ‘ubiquitous tumor’.
More than half of lipomas encountered are subcutaneous in location. Subcutaneous tissue of the trunk, nape of the neck and the limbs are the most common sites for subcutaneous lipomas.
Lipoma presents as a soft, lobulated mass enclosed by a thin, fibrous capsule.
Other fatty tumors
- Lipoblastomas are found exclusively in infants and children. They have a benign clinical course and a low recurrence rate after excision.
- Hibernomas – Tumors of brown fat arising in the back, hips, or neck in adults and infants.
- Atypical lipomatous tumors – Low-grade sarcomas; these have little metastatic potential but high chances of recurrence
- Liposarcomas – True mesenchymal malignancies.
Lipomas occur in 1% of the population.
Exact etiology of lipomas remains uncertain
Types of Lipoma
Mainly there are three varieties
- Encapsulated lipoma
- Diffuse lipoma
- Multiple lipomas
Encapsulated Lipoma
These lipomas are circumscribed encapsulated soft masses, made nearly entirely of fat. Sometimes other tissues like blood vessels [angiolipoma], muscle fibers [intramuscular lipoma], fibrous tissue [fibrolipoma], neural tissue [neurolipoma] may be present.
Diffuse Lipoma
This is a rare variety and does not possess the typical features of lipoma, hence it is often called pseudolipoma. It is seen in the subcutaneous and intramuscular tissues of the neck. It is not a typical tumor but an overgrowth of the fat in this region.
It does not possess the capsule which is typical of a lipoma. It gives rise to a disfiguring swelling at the neck.
Multiple Lipomas
Presence of multiple lipomas is also called lipomatosis. The tumors remain small or moderate in size and are sometimes painful as these often contain nerve tissue and are called neurolipomatosis. These are mostly seen in the limbs and in the trunk.
Lipomata of different sizes and shapes may be seen. Macroscopically and microscopically these are not different from solitary lipoma.
Multiple lipomas can be associated with hereditary multiple lipomatosis, Gardner’s syndrome, and Madelung’s disease.
Dercum’s disease (adiposis dolorosa) is a variety of this condition in which there are tender lipomatous swellings particularly affecting the trunk.
Anatomical Locations of Lipoma
Subcutaneous
This is the commonest variety. Although any part of the body can be affected, yet it shows a particular tendency to occur in the back, nape of the neck and on the shoulders. Subcutaneous lipoma is usually sessile but occasionally may become pedunculated. The characteristic features of such lipoma are described below.
Subfascial
Lipoma may occur under the palmar or plantar fascia and is often mistaken as tuberculous tenosynovitis. Such lipomas may also occur in the areolar layer under the epicranial aponeurosis in the scalp. Subfascial lipoma can be confused with a dermoid cyst, particularly so, as such lipoma may also erode the underlying bone as the dermoid cyst. Treatment is urgent excision of the tumor.
Intermuscular
Such lipoma occurs between the adjacent muscles and becomes firmer on feel when the adjacent muscles contract. Mechanical interference with the action of the muscles is often complained of. Fibrosarcoma is also common in such a situation and is difficult to differentiate from this condition clinically. Intermuscular lipoma is mostly seen in the thigh or around the shoulder. Treatment is early excision as it is difficult to differentiate from fibrosarcoma.
Subserous
This is rare and is sometimes found beneath the pleura or peritoneum. When it is beneath the pleura, it presents as a benign thoracic tumor. Retroperitoneal lipoma is also rare and is often misdiagnosed as hydronephrosis, pancreatic cyst or teratomatous cyst. A retroperitoneal lipoma may attain a big size. Very occasionally, one may find a lipomatous mass rather than a lipoma at the fundus of the sac of a femoral hernia. This is a condensation of extraperitoneal fat rather than a typical lipoma.
Submucous
It is also rare. It may occur in the respiratory or alimentary tract. It is also seen in the tongue. In the respiratory tract, it may cause respiratory obstruction. In the intestine, it may lead to intussusception.
Intra-articular
It occurs inside the joint and is extremely rare.
Subsynovial
Such lipomas occur deep to the synovial membrane in the fatty pad. It is seen in the knee joint. In this case, it is often confused with Baker’s cyst or bursitis.
Parosteal
It occurs under the periosteum of a bone.
Extradural
This is a type of spinal tumor. Intracranial lipoma does not occur as there is no fat in the extradural tissue within the skull.
Intraglandular
There are 3 glands in which a lipoma may be seen (i) the breast (ii) the pancreas and (iii) under the renal capsule.
Lipomas may develop in virtually all organs throughout the body including the thyroid, adrenal glands, pancreas, parathyroid glands, intralingual, parotid, orbitonasal, maxillary sinusoidal, and parapharyngeal space. Mediastinum, uterus, ovaries, and broad ligament, heart, superior vena cava, brain, and spinal cord are also known to be involved.
Presentation of Lipoma – Symptoms, and Signs
Lipoma often does not cause any symptoms. In cases of subcutaneous lipoma, a concerned patient may present with a nonpainful, palpable or visible swelling.
Symptoms in other sites depend on the location
- Airways – respiratory problems related to bronchial obstruction, aspiration and respiratory infections
- Oropharynx – swallowing discomfort or airway difficulty at the time of intubation
- Esophageal – dysphagia, regurgitation, vomiting, and reflux
- Mediastinal – impingement on the superior vena cava can lead to superior vena cava syndrome
- Intestinal – obstruction, intussusception, volvulization or hemorrhage
- Joint – joint dysfunction and pain
- Spinal cord – cord compression
On examination, subcutaneous lipoma is a soft to firm swelling and the overlying skin is freely mobile. When one gently slides the fingers off the edge of the tumor, the tumor is felt to slip out from under. This is called slip sign or slippage sign.
Differential Diagnosis
- Sebaceous cyst
- Abscess
- Hibernomas
- Angiomyolipomas
Lab Studies
Plasma D-dimer level could contribute to the differentiation between lipoma and well-differentiated liposarcoma.
Fine needle aspiration cytology (FNAC)
In this, a fine needle is inserted inside the swelling. The material aspirated is spread on a glass slide which is then stained and examined under the microscope. FNAC of lipoma reveals fragments of mature adipose tissue in a background of fat spaces and fat vacuoles. The test can be performed not only on swellings which are visible and palpable but also on those which are within the internal organs (Ultrasound or Ct guided FNAC)
Imaging Studies
No imaging studies are required in most subcutaneous lipomas.
Lesions in the gastrointestinal tract may be visible on contrast studies.
For atypical locations, ultrasonography, computed tomography, and magnetic resonance imaging could aid in diagnosis.
Ultrasound
Lipoma appears as a soft mass with variable echogenicity.
Heterogenous echotexture or large size may raise the suspicion of liposarcoma.
CT
CT shows low attenuation though it cannot reliably differentiate between lipoma and liposarcoma.
MRI
MRI is the imaging choice for lipomas and also to differentiate it from liposarcoma.
Lipomas follow subcutaneous fat signal on all sequences.
Biopsy
A part or whole of the swelling is excised and then examined by a pathologist under the microscope. It is the gold standard investigation to reliably distinguish between lipoma and liposarcoma.
Treatment
Lipomas are not amenable to any drug treatment. They need to be removed if required.
Indications for Lipoma Removal
Lipomas are removed for the following reasons:
- Cosmetic
- Confirmation of diagnosis and to rule out liposarcoma
- When they are the cause of symptoms
- Size > 5 cm
Lipomas must be removed through an extracapsular plane along with the capsule to avoid the risk of recurrence. In the case of large lipoma or suspicious lesions, a biopsy must be done to confirm/rule out the diagnosis.
In case of gastrointestinal tract, endoscopic removal can be done if feasible, otherwise, surgical removal may be done
For unusual locations, the method of removal must be according to site and approach of the tumor.
Prognosis of Lipoma
Lipoma carries an excellent prognosis. Recurrence is uncommon unless the excision was incomplete.
1