Lipoma:  

Definition

A lipoma is a benign tumour arising from yellow/white adipose tissue

It is the most common soft tissue tumour.  Hence, a lipoma is often referred to as the "universal tumour" or "ubiquitous tumour." 

 Since mature fat cells are distributed almost everywhere in the body, a lipoma can theoretically arise wherever fat tissue is present. 

Organs/Sites in Which Lipoma Cannot Occur

 1. The brain, which lacks adipose tissue and is therefore essentially the only major organ in which a true lipoma cannot arise.

2. The upper eyelid – the upper eyelid characteristically lacks subcutaneous fat. 

Ten Anatomical Planes in which Lipoma can occur are:-

1. Subcutaneous – the most common site, found in the superficial fascia
2. Subfascial – beneath deep fascia
3. Intermuscular – between muscle bellies, often diffuse and poorly encapsulated
4. Intramuscular – within the substance of a muscle
5. Subserous or Submucosal – beneath the mucosa of the gastrointestinal tract 
6. Retroperitoneal – can achieve large sizes before becoming symptomatic
7. Subsynovial – within joint spaces
8. Extradural – within the spinal canal 
9. Subperiosteal – beneath the periosteum
10. Intraglandular – within the substance of a gland, e.g., breast, parotid, or pancreas

• A submucosal lipoma of the bowel lies beneath the mucosa, and it can act as a pathological lead point for intussusception.
•  Intraglandular Lipoma can occur in the mammary gland or in the Breast.
•  Lipoma of the Spermatic Cord is the extension of extraperitoneal (properitoneal) fat through the deep inguinal ring, often encountered during open surgical repair of an inguinal hernia.  

Clinical Features of Lipoma

• Painless, slow-growing swelling, often noticed incidentally.
• Consistency is typically soft 
• Slip sign - the edge of the lipoma slips away from the palpating finger, a hallmark clinical sign 
• Lobulated surface, best appreciated on careful palpation due to fat lobules
• Mobility over underlying structures unless it is subfascial or intermuscular
• Pseudo-fluctuation - a well-known and frequently misinterpreted clinical sign

Basis of Pseudofluctuation in Lipoma

• Adipose tissue behaves as a fluid at normal body temperature rather than a rigid solid. This causes fluctuation in one direction
• True fluctuation (positive in at least two perpendicular planes due to genuine fluid transmission, as in a cyst or abscess)

Which Type of Lipoma Is Associated with Pain?

1. Angiolipoma-the pain is attributed to the presence of thrombosed vessels within the vascular component irritating adjacent nerve fibres, as well as to distension of the capsule from the increased vascularity.

2.  Dercum's disease (adiposis dolorosa), a rare condition characterised by multiple, painful subcutaneous lipomas

3. Neurolipoma (lipoma with nerve fibres traversing or embedded within it, e.g., in relation to a peripheral nerve) may also present with pain due to nerve compression or infiltration

"A painless lipoma is the rule; angiolipoma and Dercum's disease are the two classical exceptions."

Complications of lipoma

1. Pressure effects – on nerves- neurological symptoms like paresthesia, on veins- venous oedema and on arteries -arterial insufficiency.
2. Saponification – calcification following fat necrosis, seen in old or traumatized lipomas
3. Myxomatous degeneration – mucoid softening within the tumour
4. Calcification – dystrophic calcification within necrotic areas
5. Intestinal obstruction/intussusception – when submucosal lipomas of the gastrointestinal tract act as a lead point; a large pedunculated subserosal lipoma can occasionally cause volvulus
6. Malignant Transformation- Liposarcoma – the risk factors for Liposarcoma are

               Size greater than 5 cm 

               Deep-seated location

               Rapid increase in size

               Change in consistency-firm or hard

               Fixity to surrounding structures 

               Recurrent after excision 

Common sites of liposarcoma include:

• Retroperitoneum 
• Thigh  – particularly the deep intermuscular planes
• Popliteal fossa
• Shoulder girdle

Life-Threatening Complication of Lipoma

    Intussusception leading to acute intestinal obstruction and strangulation, occurring when a submucosal lipoma of the small or large bowel.

Treatment of Lipoma 

    Enucleation under anaesthesia.

    Extra-capsular excision when there is a suspicion of malignancy.

What is Hibernoma?

A benign tumour that arises from brown adipose tissue is called hibernoma. 

Common sites of brown adipose tissue in the human body include:

• Interscapular region 
• Axilla
• Mediastinum

The Classical Surgical Dictum: "When in Doubt, Clinch on Fat"

Lipoma may be considered as the differential diagnosis of a swelling when there is a diagnostic dilemma during clinical examination.

Key Points 

• Lipoma is called the "universal" or "ubiquitous" tumour because it can arise wherever fat is present — in virtually every tissue plane and organ except the brain — making its anatomical range wider than that of almost any other tumour
• Lipoma is the most common benign soft tissue tumour, arising from white/yellow adipose tissue
• Consistency is classically soft - a change to firm/hard consistency should raise suspicion
• Remember the "slip sign" as the hallmark clinical sign
• Pseudofluctuation occurs due to the semi-solid, deformable nature of fat lobules transmitting pressure - not true fluid transmission
• Angiolipoma is the classical painful lipoma variant — pain arises from thrombosed vessels within the vascular component; Dercum's disease is the other important cause of painful lipomas
• Brain and upper eyelid are both favourite exam answers for "sites where lipoma cannot occur" 
•  Submucosal lipoma lies beneath the mucosa and can cause intussusception- a life-threatening complication!
• Intraglandular lipoma of the breast must be differentiated from fibroadenoma and phyllodes tumour
• Spermatic cord lipoma commonly mimics or coexists with inguinal hernia, usually seen during open hernia surgery
• Liposarcoma usually arises de novo rather than from malignant change in an existing lipoma; the retroperitoneum and thigh are the commonest sites
• Know the red flags for liposarcoma: size >5 cm, rapid growth, deep location, fixity, recurrence after surgery & a change in the consistency.
• Local pressure effects- arterial insufficiency, venous oedema or neurological symptoms
• Hibernoma arises from brown fat, not white fat -remember interscapular, axillary, and mediastinal sites
• Treatment of choice: enucleation. Wide local excision - complete removal with the capsule and a margin of normal tissue, when there is a suspicion of malignancy.
• Remember "When in doubt, clinch on fat" for making a clinical diagnosis of a swelling/ lump.

References

1. Williams NS, O'Connell PR, McCaskie AW (eds). Bailey & Love's Short Practice of Surgery, 28th Edition. CRC Press.
2. Townsend CM, Beauchamp RD, Evers BM, Mattox KL (eds). Sabiston Textbook of Surgery, 21st Edition. Elsevier.
3. Brunicardi F, et al. (eds). Schwartz's Principles of Surgery, 11th Edition. McGraw-Hill.

Disclaimer: This post is intended for educational purposes for medical students and healthcare professionals. It does not replace clinical judgment or direct patient examination.