Definition/General
Introduction:
Soft tissue leiomyoma is a benign smooth muscle tumor
It accounts for 2-3% of soft tissue tumors
Shows mature smooth muscle differentiation
FNAC demonstrates spindle cells with smooth muscle features.
Origin:
Arises from smooth muscle cells in soft tissues
Can originate from vascular walls
Cutaneous and subcutaneous locations common
Originates from arrector pili muscles (piloleiomyoma)
Deep soft tissue involvement rare.
Classification:
WHO classification: Benign smooth muscle tumor
Subtypes include: Piloleiomyoma (cutaneous)
Angioleiomyoma (vascular)
Leiomyoma of deep soft tissue
Genital leiomyoma.
Epidemiology:
Peak incidence in 3rd-5th decades
Female predominance (2:1) for genital types
Male predominance for piloleiomyoma
Accounts for <1% of soft tissue FNAs
Familial leiomyomatosis (rare).
Clinical Features
Presentation:
Small, firm nodule (piloleiomyoma)
Painful lesion (characteristic)
Cold sensitivity (piloleiomyoma)
Tender mass
Size usually <2 cm
Well-circumscribed mass.
Symptoms:
Pain (most characteristic symptom)
Cold-induced pain (piloleiomyoma)
Pressure sensitivity
Burning sensation
Symptoms worsen with emotional stress
Hormonal influence (genital types).
Risk Factors:
Female gender (genital types)
Hormonal factors (estrogen/progesterone)
Hereditary leiomyomatosis and renal cell cancer syndrome
FH gene mutations
Previous trauma (rare)
Age 20-50 years.
Screening:
Clinical examination for tender nodules
Family history assessment
FNAC for diagnosis
Imaging for deep-seated lesions
Genetic counseling if multiple lesions
Hormonal assessment if indicated.
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Gross Description
Appearance:
Well-circumscribed nodule
Firm consistency
Gray-white cut surface
Whorled appearance
Size usually 0.5-2 cm
No necrosis or hemorrhage.
Characteristics:
Encapsulated or well-demarcated
Homogeneous cut surface
Firm to hard consistency
Gray-white to tan color
Fascicular pattern on cut surface
Smooth surface.
Size Location:
Skin and subcutis (piloleiomyoma)
Extremities most common
Trunk and head/neck
Genital region (genital leiomyoma)
Size: 0.5-3 cm (average 1-2 cm)
Multiple lesions in familial cases.
Multifocality:
Solitary in 80% cases
Multiple lesions in familial leiomyomatosis
Clustered arrangement (piloleiomyoma)
Bilateral distribution possible
Segmental pattern along nerve distribution
Hereditary patterns.
Microscopic Description
Histological Features:
FNAC shows cohesive fascicles of spindle cells
Elongated nuclei with blunt ends
Abundant eosinophilic cytoplasm
Cigar-shaped nuclei
No cellular atypia
Minimal mitotic activity.
Cellular Characteristics:
Uniform spindle cells
Elongated, blunt-ended nuclei
Fine chromatin
Abundant cytoplasm
Eosinophilic cytoplasm
Well-defined cell borders
No pleomorphism.
Architectural Patterns:
Fascicular arrangement
Interlacing bundles
Cohesive cell groups
Streaming pattern
Parallel nuclear alignment
Clean background
Minimal single cells.
Grading Criteria:
Benign cytological features
No grading system applicable
Assessment criteria: Nuclear uniformity
Cellular cohesion
Absence of atypia
Low mitotic index
Smooth muscle morphology.
Immunohistochemistry
Positive Markers:
Smooth muscle actin (SMA) - strongly positive
Desmin - positive
Calponin - positive
h-Caldesmon - positive
Vimentin - positive
Muscle-specific actin - positive.
Negative Markers:
S-100 protein - negative
CD34 - negative
Cytokeratin - negative
EMA - negative
CD68 - negative
MyoD1 - negative (vs rhabdomyosarcoma).
Diagnostic Utility:
SMA and desmin confirm smooth muscle differentiation
h-Caldesmon specific for smooth muscle
Distinguishes from other spindle cell tumors
Ki-67 low (<2%)
p53 negative
Estrogen/Progesterone receptors may be positive.
Molecular Subtypes:
Conventional leiomyoma: Standard smooth muscle markers
Epithelioid variant: Same markers, different morphology
Angioleiomyoma: Additional vascular markers
Cellular leiomyoma: Higher cellularity, same markers
Bizarre leiomyoma: Atypia but benign behavior.
Molecular/Genetic
Genetic Mutations:
FH gene mutations (hereditary leiomyomatosis)
Chromosome 1q42-43 (FH gene location)
Fumarate hydratase deficiency
HMGA2 rearrangements (some cases)
Simple karyotype in most cases
MED12 mutations (uterine types).
Molecular Markers:
Fumarate hydratase enzyme deficiency
2-Succinocysteine accumulation
HIF-1α stabilization
Krebs cycle disruption
Pseudohypoxic signature
Low mutational burden.
Prognostic Significance:
Excellent prognosis
No malignant potential
Local recurrence <5% after complete excision
No metastatic risk
Familial cases may develop renal cell carcinoma
Long-term cure expected.
Therapeutic Targets:
Complete surgical excision curative
No adjuvant therapy required
Symptom management for pain
Calcium channel blockers for piloleiomyoma pain
Genetic counseling for familial cases
Regular screening for renal tumors (HLRCC).
Differential Diagnosis
Similar Entities:
Leiomyosarcoma
Neurofibroma
Schwannoma
Fibroma
Spindle cell lipoma
Solitary fibrous tumor
Myofibroma
Dermatofibroma.
Distinguishing Features:
Leiomyoma: SMA+, desmin+, no atypia, low Ki-67
Leiomyosarcoma: Cellular atypia, high mitoses, necrosis
Neurofibroma: S-100+, loose texture, wavy nuclei
Schwannoma: S-100+ strong, Antoni A/B areas
Fibroma: Collagenous, CD34 variable
Spindle cell lipoma: CD34+, adipose component.
Diagnostic Challenges:
Distinguishing from leiomyosarcoma (requires histology)
Cellular leiomyoma vs low-grade leiomyosarcoma
Bizarre leiomyoma with nuclear atypia
Sampling adequacy in FNAC
Other spindle cell tumors
Site-specific considerations.
Rare Variants:
Epithelioid leiomyoma
Cellular leiomyoma
Bizarre (atypical) leiomyoma
Angioleiomyoma
Myxoid leiomyoma
Leiomyoma with fatty change.
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
Fine needle aspiration from [site], [size] cm firm nodule
Clinical History
[age]/[sex] with [duration] history of tender/painful nodule at [site]. [Associated symptoms].
Gross Examination
Aspirated material: [amount] of cellular material
Microscopic Examination
Smears show cohesive fascicles of uniform spindle cells with elongated, blunt-ended nuclei and abundant eosinophilic cytoplasm. No cellular atypia or mitotic activity seen. Clean background.
Immunocytochemistry
SMA: Positive, Desmin: Positive, S-100: Negative, CD34: Negative
Cytological Diagnosis
Cytological features consistent with LEIOMYOMA
Comments
The cytological and immunocytochemical features support benign smooth muscle tumor. Complete excision recommended if symptomatic. Clinical correlation advised.