Definition/General
Introduction:
Gastric leiomyoma is a benign smooth muscle tumor arising from the gastric wall
It is much less common than GIST in the stomach
Represents less than 5% of gastric mesenchymal tumors
True leiomyomas must be distinguished from leiomyomatous GIST variants.
Origin:
Arises from smooth muscle cells of the gastric wall
Most commonly from the muscularis propria layer
Can also originate from muscularis mucosae
May arise from vascular smooth muscle (vascular leiomyoma variant)
Benign proliferation of smooth muscle without malignant potential.
Classification:
Classified as conventional leiomyoma (most common)
Vascular leiomyoma (angiomyoma)
Epithelioid leiomyoma (rare variant)
Symplastic leiomyoma with degenerative atypia
Distinguished from leiomyosarcoma by lack of significant mitotic activity.
Epidemiology:
Peak incidence in 4th-6th decades
Female predominance (2:1 ratio)
Rare in children and adolescents
Higher frequency in patients with uterine leiomyomas
Sporadic occurrence in most cases.
Clinical Features
Presentation:
Asymptomatic in small tumors (<2 cm)
Dyspepsia and epigastric discomfort (40-50%)
Early satiety and bloating (30-40%)
Gastrointestinal bleeding (20-30%)
Palpable mass in large tumors
Obstruction symptoms rare.
Symptoms:
Upper GI bleeding from mucosal ulceration
Iron deficiency anemia from chronic bleeding
Postprandial pain and fullness
Nausea and vomiting (20-30%)
Weight loss uncommon unless large
Acute bleeding may require emergency intervention.
Risk Factors:
Female gender (estrogen influence)
Reproductive age (hormonal factors)
Concurrent uterine leiomyomas
Genetic predisposition (rare familial cases)
Estrogen replacement therapy
Previous smooth muscle tumors.
Screening:
No routine screening protocols
Upper endoscopy for GI symptoms
CT imaging for characterization
MRI may help differentiate from GIST
Endoscopic ultrasound for small submucosal lesions
Biopsy for definitive diagnosis.
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Gross Description
Appearance:
Well-circumscribed nodular mass with smooth surface
Gray-white cut surface with whorled pattern
Firm consistency
Encapsulated or pseudoencapsulated
Intramural location most common.
Characteristics:
Homogeneous cut surface with characteristic fascicular pattern
Absence of necrosis in typical cases
Calcification may be present in older lesions
Cystic degeneration rare
Hemorrhage uncommon unless ulcerated.
Size Location:
Size typically 1-5 cm (larger than 10 cm rare)
Antrum and body most common locations
Intramural (60-70%), subserosal (20-30%), submucosal (10-20%)
Pedunculated lesions may occur.
Multifocality:
Usually solitary (>95% cases)
Multiple leiomyomas rare but reported
Associated with uterine leiomyomas in some women
No metastatic potential
Local recurrence extremely rare after complete excision.
Microscopic Description
Histological Features:
Composed of interlacing fascicles of mature smooth muscle cells
Spindle-shaped cells with eosinophilic cytoplasm
Blunt-ended nuclei with smooth nuclear contours
Minimal nuclear pleomorphism
Low cellularity with abundant collagenous stroma.
Cellular Characteristics:
Mature smooth muscle cells with elongated nuclei
Abundant eosinophilic cytoplasm
Cigar-shaped nuclei with smooth contours
Uniform cellular morphology
Absence of significant atypia
Rare mitotic figures (<2/10 HPF).
Architectural Patterns:
Interlacing fascicular pattern
Whorled arrangement of smooth muscle bundles
Rich collagenous stroma
Prominent blood vessels throughout
No infiltrative growth
Well-demarcated borders.
Grading Criteria:
Benign tumors by definition
Mitotic count <2/10 HPF
Absence of coagulative necrosis
No significant nuclear atypia
Well-demarcated margins
Tumors with mitoses >5/10 HPF should be classified as leiomyosarcoma.
Immunohistochemistry
Positive Markers:
Smooth muscle actin (100% positive)
Desmin (95-100% positive)
Caldesmon (90-95% positive)
Muscle-specific actin (95-100%)
Calponin (80-90% positive)
Vimentin (positive).
Negative Markers:
KIT (CD117) (negative)
DOG-1 (negative)
CD34 (negative)
S-100 (negative)
Cytokeratins (negative)
Myogenin (negative).
Diagnostic Utility:
Smooth muscle markers confirm diagnosis
Desmin and SMA are most reliable
KIT negativity distinguishes from GIST
S-100 negativity excludes schwannoma
Low Ki-67 (<5%) supports benign nature.
Molecular Subtypes:
No established molecular subtypes
Hormone receptor expression (estrogen, progesterone) may be present
No specific genetic alterations
Chromosomal aberrations rare
Gene expression profile distinct from GIST.
Molecular/Genetic
Genetic Mutations:
No consistent genetic alterations
Chromosomal rearrangements uncommon
TP53 mutations absent
KIT/PDGFRA mutations absent (distinguish from GIST)
Microsatellite stability
Low mutational burden.
Molecular Markers:
Low proliferation index (Ki-67 <5%)
p53 overexpression absent
MDM2 amplification absent
Hormone receptor expression may be present
VEGF expression variable
Apoptosis markers low.
Prognostic Significance:
Excellent prognosis with complete excision
No malignant transformation potential
Size >10 cm may indicate increased surveillance
Mitotic activity >2/10 HPF warrants careful evaluation
Recurrence extremely rare.
Therapeutic Targets:
Surgical excision is curative
Enucleation for small tumors
Wedge resection for larger lesions
No adjuvant therapy required
Hormonal therapy not indicated
Targeted therapy not applicable.
Differential Diagnosis
Similar Entities:
Gastrointestinal stromal tumor (GIST)
Leiomyosarcoma
Schwannoma
Inflammatory myofibroblastic tumor
Solitary fibrous tumor
Desmoid fibromatosis.
Distinguishing Features:
Leiomyoma: Desmin positive, KIT negative
Leiomyoma: Low mitotic count
GIST: KIT and/or DOG-1 positive
Leiomyosarcoma: High mitotic count >5/10 HPF
Schwannoma: S-100 positive, desmin negative
IMT: ALK positive in 50%.
Diagnostic Challenges:
Distinguishing from leiomyomatous variant of GIST
Separating from low-grade leiomyosarcoma
Identifying degenerative atypia vs true malignancy
Sampling adequacy for mitotic count assessment.
Rare Variants:
Vascular leiomyoma (angiomyoma) with prominent vasculature
Epithelioid leiomyoma with epithelioid morphology
Symplastic leiomyoma with degenerative nuclear atypia
Lipoleiomyoma with mature fat component.
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
[specimen type], measuring [size] cm in greatest dimension
Diagnosis
Leiomyoma
Size and Location
Size: [X] cm, Location: [intramural/submucosal/subserosal]
Histological Features
Mature smooth muscle cells in fascicular pattern, minimal atypia
Mitotic Count
Mitotic count: [X] mitoses per 10 high-power fields (consistent with benign tumor)
Immunohistochemistry
Desmin: positive, Smooth muscle actin: positive, KIT: negative
Margins
Surgical margins: [negative/positive], closest margin: [X] mm
Benign Features
Low mitotic count, no necrosis, minimal nuclear atypia, well-demarcated
Final Diagnosis
Gastric leiomyoma, [size] cm, margins [status]