Challenges in Diagnosing Cribriform Morular Thyroid Carcinoma

Cribriform morular thyroid carcinoma (CMTC) is a rare thyroid malignancy strongly associated with familial adenomatous polyposis (FAP). About 50% of CMTC cases are associated with FAP, including a subset in which CMTC is the presenting symptom in previously undiagnosed FAP. We present a case of a young woman with thyroid nodules monitored for several years due to low suspicion ultrasound features. After development of macrocalcifications in 1 nodule, she had a fine needle aspiration (FNA). The cytology was concerning for papillary thyroid carcinoma. She underwent total thyroidectomy with final pathology of CMTC. Given the strong association between CMTC and FAP, the patient completed endoscopy, colonoscopy, and genetic testing, which led to a diagnosis of FAP. The diagnosis of CMTC can be difficult because nodules are often small without concerning ultrasound features, not meeting recommendations for FNA. Due to an increased risk of CMTC in individuals with FAP, current criteria may be inadequate in identifying nodules warranting thyroid FNA. Continued ultrasound surveillance should be considered for nodules with low suspicion ultrasound features in this population.