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Fine needle aspiration cytologic characteristics of hyalinizing trabecular adenoma of the thyroid
1Department of Pathology, University Hospital, London, Ontario, Canada.
Insights
A rare hyalinizing trabecular adenoma was initially misdiagnosed as malignant thyroid cancer. Final histology confirmed the benign nature, validating the initial negative cytologic diagnosis.
Area of Science:
- Endocrinology
- Cytopathology
- Surgical Pathology
Background:
- Thyroid nodules present a diagnostic challenge, requiring accurate differentiation between benign and malignant conditions.
- Hyalinizing trabecular adenoma (HTA) is a rare thyroid tumor that can mimic malignant neoplasms cytologically and histologically.
- Accurate diagnosis is crucial for appropriate patient management and treatment strategies.
Observation:
- A solitary thyroid nodule initially diagnosed as benign on fine needle aspiration (FNA) showed features concerning for malignancy on frozen section.
- Cytologic findings included increased cellularity, mild nuclear atypia, and eosinophilic nuclear pseudoinclusions.
- Histologic examination revealed a poorly differentiated pattern with marked nuclear atypia and fibrous stroma, initially suggestive of medullary carcinoma.
Findings:
- Immunopathology and electron microscopy ruled out medullary carcinoma.
- Subsequent review of the histology led to the recategorization of the tumor as a hyalinizing trabecular adenoma.
- This case highlights the potential for discrepancy between initial cytologic and intraoperative frozen section diagnoses.
Implications:
- Accurate cytologic evaluation is vital for diagnosing rare thyroid tumors like HTA.
- Understanding the cytologic features of HTA can prevent misdiagnosis and unnecessary aggressive treatment.
- This case underscores the importance of comprehensive review in surgical pathology for definitive diagnosis.
Abstract:
The cytologic characteristics of a histologically proven hyalinizing trabecular adenoma are presented. The solitary thyroid nodule was diagnosed cytologically as benign and histologically as malignant. Cytologically, the fine needle aspirate showed increased cellularity, with mild nuclear atypia and eosinophilic nuclear pseudoinclusions. Collections of an amorphous colloidlike material were noted surrounded by follicular cells. Inflammatory cells in the background suggested the possibility of a thyroiditis. Since the patient's antibodies were negative, a hemithyroidectomy was performed to rule out a neoplasm. The frozen section was interpreted as suggestive of medullary carcinoma since the tumor showed a poorly differentiated pattern of cells with marked nuclear atypia and abundant fibrous stroma (thought to be amyloid) separating the cells. The results of immunopathology and electron microscopy ruled out a medullary carcinoma. Upon review of the histology at a later date, the case was recategorized as a hyalinizing trabecular adenoma, proving the negative cytologic diagnosis to be correct.