Definition/General
Introduction:
Small intestinal lipoma is a benign tumor composed of mature adipose tissue
It represents the third most common benign small bowel tumor after leiomyoma and adenoma
It shows slow growth and excellent prognosis
It can cause intussusception if large.
Origin:
Arises from mature adipocytes in the bowel wall
Most commonly originates from submucosal layer
Can arise from subserosal adipose tissue
Results from localized proliferation of fat cells
Hormonal factors may influence growth.
Classification:
Based on location: submucosal (most common), subserosal, intramural
Based on size: small (<2 cm), large (>2 cm)
Solitary vs multiple
Pedunculated vs sessile.
Epidemiology:
Rare small bowel tumors (2-3% of benign tumors)
Female predominance (2:1 ratio)
Peak incidence: 50-70 years
Ileum most common location (75%)
Usually solitary.
Clinical Features
Presentation:
Often asymptomatic (small lipomas)
Abdominal pain (most common symptom)
Intussusception (large lipomas, 70% cases)
Small bowel obstruction
GI bleeding (rare)
Palpable mass (large lesions).
Symptoms:
Crampy abdominal pain
Nausea and vomiting
Intestinal obstruction symptoms
Change in bowel habits
Occult bleeding (uncommon)
Early satiety (large tumors).
Risk Factors:
Female sex
Advanced age (50-70 years)
Obesity
Genetic predisposition (rare familial cases)
Multiple endocrine neoplasia (very rare association).
Screening:
CT scan (characteristic fat density -50 to -100 HU)
MRI (T1 and T2 hyperintense)
Upper endoscopy (duodenal lesions)
Capsule endoscopy
Double-balloon enteroscopy.
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Gross Description
Appearance:
Yellow, soft tumor
Lobulated surface
Encapsulated or well-circumscribed
Homogeneous cut surface
Greasy consistency
Floating in formalin (low density).
Characteristics:
Well-demarcated from surrounding tissue
Smooth, lobulated contour
Yellowish coloration
Soft, compressible
Homogeneous appearance
No hemorrhage or necrosis.
Size Location:
Ileum (75% of cases)
Jejunum (20%)
Duodenum (5%)
Size range: 1-10 cm (average 3-4 cm)
Submucosal location predominant
Intussusception lead point (large lesions).
Multifocality:
Usually solitary (95% cases)
Multiple lipomas rare
May coexist with colonic lipomas
Associated with lipomatosis (very rare)
No malignant transformation.
Microscopic Description
Histological Features:
Mature adipose tissue
Uniform adipocytes with single lipid vacuole
Thin fibrous septa
Minimal stroma
Blood vessels between fat cells
No cellular atypia.
Cellular Characteristics:
Mature adipocytes
Peripheral nuclei
Single large lipid vacuole
Thin cytoplasm
Uniform cell size
No mitotic activity.
Architectural Patterns:
Lobular architecture
Thin fibrous septa dividing lobules
Vascular network
No mucosa involvement typically
Well-demarcated from surrounding tissue
Capsule may be present.
Grading Criteria:
No grading system (benign tumor)
Maturity assessment: mature vs immature fat
Cellularity evaluation
Absence of atypia
No mitotic activity.
Immunohistochemistry
Positive Markers:
S-100 (adipocytes positive)
Adipophilin (fat cell marker)
Vimentin (mesenchymal marker)
CD68 (foamy macrophages may be present)
Leptin (adipocyte marker).
Negative Markers:
Cytokeratins (excludes carcinoma)
CD117 (excludes GIST)
Desmin (excludes smooth muscle tumor)
S-100 in spindle cells (excludes schwannoma)
CDK4 (excludes liposarcoma).
Diagnostic Utility:
Confirms adipose tissue origin
Excludes liposarcoma (no atypia, no CDK4)
Distinguishes from other mesenchymal tumors
Demonstrates mature fat cells
Rules out inflammatory conditions.
Molecular Subtypes:
Conventional lipoma: mature adipose tissue
Fibrolipoma: increased fibrous tissue
Angiolipoma: prominent vascular component
Myxolipoma: myxoid areas.
Molecular/Genetic
Genetic Mutations:
HMGA2 rearrangements (some cases)
12q14-15 abnormalities
MDM2 amplification (rare)
Simple karyotype usually
Chromosomal rearrangements (uncommon).
Molecular Markers:
Adiponectin expression
Leptin production
PPAR-γ activation
Normal lipid metabolism markers
Low proliferation index.
Prognostic Significance:
Excellent prognosis
No malignant potential
Complete excision: curative
Size >5 cm: higher intussusception risk
Location: affects symptomatology.
Therapeutic Targets:
Surgical excision: complete removal
Enucleation possible for small lesions
Endoscopic removal (pedunculated lesions)
Laparoscopic approach
No adjuvant therapy needed.
Differential Diagnosis
Similar Entities:
Liposarcoma
Hibernoma
Angiomyolipoma
Inflammatory pseudotumor
Gastrointestinal stromal tumor
Schwannoma.
Distinguishing Features:
Lipoma: mature fat, no atypia
Liposarcoma: cellular atypia, CDK4+
Hibernoma: brown fat cells
Angiomyolipoma: melanoma markers+
GIST: CD117+
Schwannoma: S-100+ spindle cells.
Diagnostic Challenges:
Distinguishing from well-differentiated liposarcoma
Recognizing variants (fibrolipoma, angiolipoma)
Excluding lipomatous hamartoma
Assessing completeness of excision
Correlation with imaging findings.
Rare Variants:
Fibrolipoma
Angiolipoma
Myxolipoma
Chondroid lipoma
Pleomorphic lipoma (very rare in GI tract).
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Small bowel segment with tumor, measuring [size] cm
Diagnosis
Small intestinal lipoma
Histological Features
Well-circumscribed tumor composed of mature adipose tissue
Adipose Tissue
Mature adipocytes with single lipid vacuoles and peripheral nuclei
Cellular Features
Uniform mature fat cells without atypia or mitotic activity
Size and Location
Tumor size: [X] cm, location: [submucosal/subserosal]
Margins
Excision margins: [complete/incomplete]
Special Studies
S-100: positive (adipocytes), Vimentin: positive
No molecular studies required for typical lipoma
[other study]: [result]
Final Diagnosis
Small intestinal lipoma, [size] cm, completely excised