Definition/General

Introduction:
-Struma ovarii is a monodermal teratoma composed predominantly of thyroid tissue
-Accounts for 2-5% of mature teratomas
-Contains thyroid follicles as the major component
-May cause hyperthyroidism in 5-10% cases.
Origin:
-Originates from germ cells with specific differentiation toward thyroid tissue
-Shows predominantly thyroidal differentiation
-Contains thyroid follicles with colloid
-May have normal thyroid function or hyperthyroidism.
Classification:
-Pure struma ovarii (>50% thyroid tissue)
-Struma ovarii with other teratomatous elements
-Malignant struma ovarii (rare, <5%)
-Functioning struma (causes hyperthyroidism)
-Non-functioning struma (most common).
Epidemiology:
-Peak incidence in 4th-5th decades
-Represents 2-5% of mature teratomas
-Unilateral in >95% cases
-Hyperthyroidism occurs in 5-10%
-More common in iodine-deficient areas.

Clinical Features

Presentation:
-Asymptomatic pelvic mass (most common)
-Hyperthyroid symptoms (5-10% cases) with palpitations, weight loss
-Abdominal/pelvic pain
-Abdominal distension
-Thyrotoxicosis may be present.
Symptoms:
-Pelvic mass (70-80%)
-Hyperthyroid symptoms (palpitations, tremor, weight loss)
-Abdominal pain (40-50%)
-Heat intolerance
-Menstrual irregularities
-Anxiety and nervousness
-Asymptomatic (30-40%).
Risk Factors:
-Reproductive age
-Iodine deficiency
-Family history of thyroid disease
-Previous teratomas
-Genetic factors unclear
-Geographic variations (endemic goiter areas).
Screening:
-Thyroid function tests (TSH, T3, T4)
-Thyroglobulin levels (elevated)
-Pelvic ultrasound
-Thyroid scan (may show ovarian uptake)
-CA-125 (usually normal)
-MRI for characterization.

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Gross Description

Appearance:
-Solid, multilocular cystic mass
-Brown to green gelatinous contents (colloid-like)
-Size ranges from 5-20 cm
-Smooth capsule
-Resembles thyroid tissue on cut surface.
Characteristics:
-Unilateral in >95% cases
-Encapsulated appearance
-Cut surface shows solid areas with cystic spaces
-Brown-green gelatinous material
-Honeycomb appearance
-May have calcifications.
Size Location:
-Variable size (2-25 cm)
-Average size 8-12 cm
-No specific ovarian location preference
-Usually larger than normal teratomas
-Slow growth pattern.
Multifocality:
-Usually unifocal
-Bilateral involvement rare (<5%)
-May coexist with other teratomatous elements
-Pure thyroid tissue in some cases.

Microscopic Description

Histological Features:
-Thyroid follicles of varying sizes filled with colloid
-Follicular epithelium resembling normal thyroid
-Colloid material similar to thyroid
-May have papillary architecture
-C-cells may be present.
Cellular Characteristics:
-Cuboidal to columnar epithelium lining follicles
-Bland nuclear features in benign cases
-Eosinophilic colloid filling follicles
-Basement membrane intact
-Minimal mitotic activity.
Architectural Patterns:
-Follicular pattern (most common)
-Microfollicular pattern
-Macrofollicular pattern
-Solid pattern (rare)
-Papillary pattern (if malignant transformation).
Grading Criteria:
-Benign struma ovarii (>95%)
-Malignant struma ovarii (<5%) shows features of thyroid carcinoma
-Papillary carcinoma most common malignant type
-Follicular carcinoma rare.

Immunohistochemistry

Positive Markers:
-Thyroglobulin (95-100%)
-TTF-1 (90-95%)
-PAX8 (85-90%)
-Thyroid peroxidase (80-85%)
-Cytokeratin
-Calcitonin (C-cells if present).
Negative Markers:
-AFP (negative)
-Beta-hCG (negative)
-Inhibin (negative)
-Calretinin (negative)
-WT1 (negative)
-Chromogranin (negative except C-cells).
Diagnostic Utility:
-Thyroglobulin positivity diagnostic
-TTF-1 confirms thyroidal origin
-PAX8 supports thyroid differentiation
-Distinguish from other ovarian tumors
-Negative germ cell markers.
Molecular Subtypes:
-Similar to thyroid tumors
-RAS mutations (follicular pattern)
-BRAF mutations (papillary pattern)
-RET/PTC rearrangements (papillary)
-PAX8/PPARγ (follicular).

Molecular/Genetic

Genetic Mutations:
-RAS mutations (NRAS, HRAS, KRAS)
-BRAF V600E (papillary carcinoma)
-RET/PTC rearrangements
-PAX8/PPARγ fusion (follicular carcinoma)
-TP53 mutations (anaplastic).
Molecular Markers:
-Thyroglobulin expression
-TTF-1 expression
-PAX8 expression
-Thyroid-specific gene expression
-Similar to normal thyroid.
Prognostic Significance:
-Benign behavior in most cases
-Malignant transformation rare (<5%)
-Hyperthyroidism resolves after removal
-Excellent prognosis overall.
Therapeutic Targets:
-Surgical removal curative
-Antithyroid medications (preoperatively if hyperthyroid)
-Radioiodine therapy (malignant cases)
-Thyroid hormone suppression.

Differential Diagnosis

Similar Entities:
-Primary thyroid carcinoma metastases
-Clear cell carcinoma
-Mucinous tumors
-Other monodermal teratomas
-Thyroid tissue in normal teratoma.
Distinguishing Features:
-Struma ovarii: Predominantly thyroid tissue
-Ovarian location
-Thyroglobulin positive
-Metastatic thyroid: Known primary
-Bilateral often
-Clear cell: Different morphology
-Negative thyroid markers.
Diagnostic Challenges:
-Distinguishing benign from malignant
-Metastatic thyroid carcinoma exclusion
-Functioning vs non-functioning
-Sampling adequacy
-Thyroid correlation.
Rare Variants:
-Malignant struma ovarii
-Papillary carcinoma arising in struma
-Follicular carcinoma
-Mixed with other teratomatous elements
-Functioning struma.

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

Ovarian mass, [side], measuring [X x Y x Z] cm

Diagnosis

Struma Ovarii, [Benign/Malignant]

Classification

WHO Classification: Monodermal Teratoma, Struma Ovarii

Histological Features

Shows thyroid follicles with colloid, [X]% of tumor volume

Special Studies

IHC: Thyroglobulin [positive], TTF-1 [positive], PAX8 [positive]

Thyroid function: [normal/hyperthyroid]

Final Diagnosis

Ovarian Struma Ovarii, [Side]