Francisco Zaldana, MD and Lisa Radkay, MD
University of Texas Health Science Center
San Antonio, Texas

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Clinical History

78-year-old male with a past medical history of multiple comorbidities including type 2 diabetes mellitus (T2DM), hypertension (HTN), chronic kidney disease (CKD), and hyperlipidemia with an extensive smoking history. The patient had no significant medical family history.

On exam by the primary care physician, the thyroid felt enlarged, low lying, and with palpable left nodule. A thyroid ultrasound was obtained which demonstrated a solid hypoechoic nodule in the left thyroid lobe measuring 2.7 x 1.8 x 1.6 cm with scattered microcalcifications within the nodule, and a second slightly hypoechoic solid nodule in the right lobe measuring 1.3 cm in greatest dimension. Fine needle aspiration was performed of the left thyroid nodule, which showed the diagnosis.

Cytopathology Features

Medullary thyroid carcinoma is a relatively rare tumor that has a broad range of histologic features with many variants that overlap with other tumors in the thyroid. Most often it is described cytologically as numerous non-cohesive cells, with some loose clusters, composed of epithelioid, plasmacytoid, and/or spindle shaped cells with round or elongated nuclei, granular chromatin, inconspicuous nucleoli, with the possibility of pseudo inclusions, multiple nucleoli, red cytoplasmic granules, and amyloid [2]. Additionally, the tumor can contain entrapped benign follicular cells, and may have calcifications or psammoma bodies.

The broad morphologic features although well documented may lead to misdiagnosis by an unsuspecting pathologist, so medullary thyroid carcinoma must always be in the differential when looking at an atypical thyroid nodule, especially in cytology due to limited sampling.

Figure 1: Ultrasound of left thyroid, showing a hypoechoic nodule

Figure 2: Air dry smear (400X, Diff Quik stain) is cellular and shows loosely cohesive groups of cells with pleomorphic nuclei some with elongated/ spindled morphology. No colloid or macrophages are appreciated in the background.

Figure 3: Alcohol fixed smear (Pap stain) shows small clusters of cells with increased nuclear to cytoplasmic ratio without pseudonuclear inclusions or nuclear grooves appreciated, 600X

Figure 4: 600x H&E of cell block material obtained at time of fine needle aspiration. Cells with irregular nuclear membranes and chromatin pattern, 600X.