Cyst-like anatomical variant of the thyroid cartilage

A 48-year-old female patient was referred to the radiology department for a surveillance neck ultrasound after total thyroidectomy for papillary cancer (T1aNoMo) two years before. Serum thyroglobulin levels were normal. She presented no hoarseness, cough or dysphagia.

No findings suggestive of local or nodal recurrence of thyroid cancer were evidenced by neck ultrasound.  However, sonographic neck evaluation showed subcentimetre focal dilatations of each laminae of the thyroid cartilage with well-defined borders and hypoechoic centre. A neck MR was performed showing high signal on fat-suppressed sequences within these focal dilatations of the cartilage laminae. These findings were consistent with cystic lesions of the thyroid cartilage as an anatomical variant.

The thyroid cartilage is the largest of the nine cartilages of the larynx [2]. Its name means shield-shaped in Greek. It is formed by two lateral hyaline laminae that join ventrally to form a V-shaped cartilaginous sling [2].  From its embryological development and to advanced ages of life, it undergoes multiple processes of mineralisation and ossification starting in the posteroinferior portion of the lamina [1, 2]. This process is believed to be secondary to micro-traumatism by the extra-laryngeal musculature which leads to progressive calcification [1, 4, 5]. In certain cases, this process does not evolve completely, and the thyroid cartilage may show cyst-like cavities, especially in the anterior half [1, 2]. These cyst-like formations of the thyroid cartilage are uncommon and are usually seen as an incidental finding on imaging studies [1, 2]. They may be symmetrical, affecting both thyroid laminae, [1] and have been mainly described in adolescents [1, 2]. The differential diagnosis of these cyst-like changes in the thyroid cartilage includes degenerative cysts of the thyroid cartilage, post-traumatic [1, 2] or post-radiotherapy cysts [1], chondromas, chondrosarcomas [1, 2] or metastases [3]. Radiologists should bear in mind this infrequent anatomical variation in order to avoid misdiagnosis and further unnecessary examinations.