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

Disclosure: We do not have any affiliations or financial interests in any of the corporate organizations involved with the products to which our case study will refer.

Continuing Medical Education (CME): The American Society of Cytopathology is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians.

The American Society of Cytopathology designates this enduring educational activity for a maximum of 1 AMA PRA Category 1 credit(s).TM Physicians should only claim credit commensurate with the extent of their participation in the activity.

American Board of Pathology Continuing Certification (CC): This product can help fulfill the CME requirements and Self-Assessment Modules (SAMs) mandated by the American Board of Pathology CC process.

Continuing Medical Laboratory Education (CMLE): The ASC designates this activity for the indicated number of CMLE credit hours and also fulfills requirements of the ABMS to participate in the Maintenance of Certification program.

This program is approved for continuing education credits in the State of Florida for 1 credit and the State of California for ½ credit.

Disclosure for Education Planners

Review the Case Study and visit the ASC Web site (https://education.cytopathology.org/) to take the test for Continuing Education Credit.

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.