Cystic Medullary Thyroid Carcinoma 373 Case Report 373 Division of Anatomic Pathology and Histology, Division of Nuclear Medicine (VR), and Division of Surgery (GA), Catholic University of Sacred Heart, Rome, Italy Address correspondence to Dr. Guido Fadda, Division of Anatomic Pathology and Histology, Catholic University of Sacred Heart, Largo Francesco Vito, 1, 00168 Rome, Italy Endocrine Pathology, vol. 11, no. 4, 373–377, Winter 2000 © Copyright 2000 by Humana Press Inc. All rights of any nature whatsoever reserved. 1046–3976/00/11:373–377/ $11.25 Cystic Medullary Thyroid Carcinoma: Report of a Case with Morphological and Clinical Correlations Guido Fadda, MD, Antonino Mulè, MD, Vittoria Rufini, MD, Guglielmo Ardito, MD, Luca Revelli, MD, Marilena C. Fiorino, MD, and Arnaldo Capelli, MD Abstract Cystic lesions of the thyroid are common findings. Although many thyroid cysts are of benign, some cases of hemorrhagic degenerative changes occur in neoplastic nodules, mostly follicular neoplasms and papillary carcinomas. The occurrence of hemorrhagic changes in medullary carcinomas has never been documented with aspirative cytological and histological pictures to the best of our knowledge. A case of medullary thyroid carci- noma with a large central hemorrhagic cyst is described, and the literature regarding the pathogenesis of this regression and the occurrence of cystic neoplasms in the thyroid is reviewed. Key Words: Medullary thyroid carcinoma; thyroid pathology; fine-needle aspiration biopsy. Introduction Cystic lesions represent a large group of thyroid diseases accounting for 15–25% of all nodules [1,2]. The great majority of these cysts occur within goitrous nodules, usually as a consequence of hemorrhagic degeneration in the center of the lesion. Some cases of cystic degeneration occur within neoplastic nodules, mostly follicu- lar neoplasms, but also often in papillary carcinomas [3–9]. As a consequence, every cystic lesion of the thyroid requires an accurate evaluation to rule out the possi- bility of a cystic malignancy. Although every malignant neoplasm might present itself as a cystic lesion, this is a characteris- tic of papillary and follicular carcinomas, whereas medullary carcinoma and other epithelial and nonepithelial malignancies usually exhibit a solid pattern with necrotic areas [10,11]. A case of medullary carci- noma with cystic degeneration, diagnosed preoperatively with fine-needle aspiration biopsy (FNA), is described, and the litera- ture regarding cystic changes within thy- roid neoplasms is reviewed. Case Description A 77-yr old Caucasian female was referred to the Division of Anatomic Pathology of the Catholic University of Rome to undergo a FNA for a cystic lesion in her right thyroid lobe. A previous FNA performed in another institution aspirated a discrete amount of bloody fluid and a diagnosis of hemorrhagic cyst without atypical cells was made. However, a few weeks later the lesion had returned to its previous size. The sonographic picture showed a single encapsulated nodule of 3.7 × 3.3 cm, with central anechoic area in her right lobe and, at the same site, a radionu- clide scan with 99 m Tc-pertechnetate (3 mCi