Definition/General
Introduction:
Small intestinal leiomyoma is a benign smooth muscle tumor arising from muscularis mucosae or muscularis propria
It represents true smooth muscle neoplasm
It shows low mitotic activity and no cellular atypia
It is less common than gastric leiomyomas.
Origin:
Arises from smooth muscle cells of intestinal wall
Most commonly from muscularis propria
Can originate from muscularis mucosae
Results from benign proliferation of smooth muscle cells
Hormonal influences may play role.
Classification:
Based on size: small (<2 cm), large (>2 cm)
Based on location: intramural, subserosal, submucosal
Solitary (most common) vs multiple
Associated with hereditary leiomyomatosis (rare).
Epidemiology:
Rare tumors (<5% of small bowel neoplasms)
Female predominance (2:1 ratio)
Peak incidence: 40-60 years
Jejunum most common location (50%)
Higher incidence than leiomyosarcoma.
Clinical Features
Presentation:
Often asymptomatic (small tumors)
Abdominal pain (most common symptom)
Small bowel obstruction (20-30% cases)
GI bleeding (if mucosal ulceration)
Palpable mass (large tumors).
Symptoms:
Crampy abdominal pain
Intestinal obstruction symptoms
Occult GI bleeding (iron deficiency anemia)
Early satiety (large tumors)
Nausea and vomiting
Weight loss (obstruction cases).
Risk Factors:
Female sex (hormonal influence)
Reproductive age
Multiple leiomyomatosis syndrome
Hereditary leiomyomatosis and renal cell carcinoma (HLRCC)
Previous pelvic surgery.
Screening:
CT abdomen (well-circumscribed mass)
MRI (T2 hypointense)
Upper endoscopy (duodenal lesions)
Capsule endoscopy
Small bowel follow-through
EUS (wall layer assessment).
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Gross Description
Appearance:
Well-circumscribed mass
Firm, rubbery consistency
Gray-white cut surface
Whorled appearance
Smooth surface
Encapsulated or pseudoencapsulated.
Characteristics:
Intramural location most common
Smooth, lobulated contour
Homogeneous cut surface
Fascicular pattern visible
No necrosis or hemorrhage typically
Well-demarcated from surrounding tissue.
Size Location:
Jejunum (50% cases)
Ileum (30%)
Duodenum (20%)
Size range: 1-15 cm (average 3-5 cm)
Solitary lesions (90%)
Intramural growth pattern.
Multifocality:
Usually solitary
Multiple leiomyomas (hereditary syndromes)
Associated uterine leiomyomas common
Concurrent with other GI tract leiomyomas
Bilateral renal involvement (HLRCC syndrome).
Microscopic Description
Histological Features:
Spindle-shaped smooth muscle cells
Fascicular arrangement
Interlacing bundles
Elongated nuclei with blunt ends
Eosinophilic cytoplasm
Low mitotic activity (<2 mitoses per 10 HPF).
Cellular Characteristics:
Uniform spindle cells
Cigar-shaped nuclei
No nuclear atypia
Minimal pleomorphism
Abundant eosinophilic cytoplasm
Longitudinal striations visible
Low mitotic rate.
Architectural Patterns:
Interlacing fascicles
Whorled pattern
Perpendicular orientation of fascicles
Hyalinized areas possible
Calcifications rare
No necrosis typically.
Grading Criteria:
Mitotic count: <2 per 10 HPF (diagnostic criterion)
Nuclear atypia: absent or minimal
Cellularity: moderate
Necrosis: absent
Size: variable significance.
Immunohistochemistry
Positive Markers:
Desmin (positive, diagnostic)
Smooth muscle actin (SMA, positive)
Caldesmon (positive)
Vimentin (positive)
h-Caldesmon (high molecular weight, specific).
Negative Markers:
CD117 (KIT) (negative, excludes GIST)
DOG1 (negative, excludes GIST)
S-100 (negative, excludes schwannoma)
CD34 (negative)
Chromogranin A (negative).
Diagnostic Utility:
Confirms smooth muscle differentiation
Desmin positivity diagnostic for smooth muscle
Distinguishes from GIST (CD117-negative)
Excludes nerve sheath tumors (S-100 negative)
Confirms benign nature.
Molecular Subtypes:
Conventional leiomyoma: typical smooth muscle markers
Epithelioid variant: round cell morphology but same markers
Hereditary forms: fumarate hydratase deficiency.
Molecular/Genetic
Genetic Mutations:
FH gene mutations (hereditary leiomyomatosis)
Chromosomal rearrangements
12q14-15 deletions
HMGA2 rearrangements
MED12 mutations (some cases).
Molecular Markers:
Fumarate hydratase deficiency (HLRCC)
2-Succinocysteine accumulation
Smooth muscle-specific proteins
Low Ki-67 proliferation index
Normal p53 expression.
Prognostic Significance:
Benign behavior: no metastatic potential
Complete excision: curative
Size >5 cm: higher recurrence risk if incomplete excision
Multiple tumors: suggest genetic syndrome.
Therapeutic Targets:
Complete surgical excision
Enucleation (small tumors)
Segmental resection (large tumors)
Laparoscopic approach possible
Genetic counseling (multiple tumors).
Differential Diagnosis
Similar Entities:
Gastrointestinal stromal tumor (GIST)
Leiomyosarcoma
Schwannoma
Inflammatory myofibroblastic tumor
Fibroma
Solitary fibrous tumor.
Distinguishing Features:
Leiomyoma: desmin+, CD117-, low mitoses
GIST: CD117+, DOG1+
Leiomyosarcoma: high mitoses (>5/10 HPF), atypia
Schwannoma: S-100+
IMT: ALK+ (50% cases).
Diagnostic Challenges:
Distinguishing from low-grade leiomyosarcoma
Mitotic count accuracy
Identifying epithelioid variant
Excluding GIST (immunohistochemistry essential)
Assessing margin status.
Rare Variants:
Epithelioid leiomyoma
Leiomyoblastoma (outdated term)
Cellular leiomyoma
Hyalinized leiomyoma
Multiple intestinal leiomyomatosis.
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 resection with tumor, measuring [size] cm
Diagnosis
Small intestinal leiomyoma
Histological Features
Well-circumscribed spindle cell tumor with smooth muscle differentiation
Mitotic Activity
Mitotic count: [X] per 10 high-power fields (normal <2/10 HPF)
Size and Location
Tumor size: [X] cm, location: [intramural/subserosal/submucosal]
Margins
Resection margins: [uninvolved/involved], closest margin: [X] mm
Special Studies
Desmin: positive, SMA: positive, CD117: negative, DOG1: negative
Ki-67 proliferation index: [low percentage]
[other study]: [result]
Final Diagnosis
Small intestinal leiomyoma, [size] cm, with clear margins