Benign Tumor Composed of Mature Adipocytes Encapsulated in Fibrous Tissue: Lipoma vs Fibroma
A benign tumor composed of mature adipocytes encapsulated in fibrous tissue is definitively a lipoma, not a fibroma. 1
Characteristics of Lipomas
- Lipomas are benign neoplasms derived from adipose tissue composed of mature adipocytes 2
- They are typically encapsulated in fibrous tissue, creating a well-circumscribed mass 3
- Histologically, lipomas consist of mature adipocytes that are relatively uniform in size and lack cytologic atypia 1
- They account for approximately 1% of gastric intramural lesions but are more common in subcutaneous tissues 1
Diagnostic Features of Lipomas
- On endoscopic ultrasound (EUS), lipomas appear as intensely hyperechoic, well-circumscribed masses arising from the submucosal wall layer (3rd layer) 1
- On endoscopy, lipomas often have a yellow hue and exhibit a "pillow sign" when probed with closed biopsy forceps 1
- The pillow sign has high specificity (98%) but lower sensitivity (40%) for identifying lipomas 1
- Lipomas may also exhibit some mobility when probed 1
Distinguishing Lipomas from Fibromas
- Fibromas are composed primarily of fibrous tissue (collagen-producing fibroblasts), not adipocytes 4
- While lipomas contain fibrous tissue as an encapsulating component, their main cellular component consists of mature adipocytes 3
- The presence of mature adipocytes as the primary cellular component is the defining characteristic that makes this a lipoma rather than a fibroma 1
Clinical Significance
- Lipomas are typically benign, slow-growing lesions but can cause clinical symptoms in some cases 1
- Symptoms may include bleeding (if ulceration occurs), obstruction, or pain depending on location and size 1
- Most lipomas present as solitary lesions, though multiple lipomas can occur 1, 5
- Lipomas can be found in various locations including subcutaneous tissues, gastrointestinal tract, and other organs 5
Management Considerations
- For asymptomatic, small lipomas with classic imaging features, observation may be appropriate 4
- For symptomatic lipomas or those with uncertain diagnosis, complete surgical excision is the standard treatment 4
- The recurrence rate for properly excised lipomas is low 4
Important Distinctions
- It's important to distinguish benign lipomas from atypical lipomatous tumors (ALT) or liposarcomas 4
- Features suggesting ALT include nodularity, septations, stranding, and larger size 4
- Definitive diagnosis in uncertain cases may require molecular testing for MDM-2 amplification 4
In summary, the histological description of mature adipocytes encapsulated in fibrous tissue is the classic definition of a lipoma, not a fibroma, which would be primarily composed of fibrous tissue.