The prevalence and features of thyroid pyramidal lobes as assessed by computed tomography

The pyramidal lobe is an accessory lobe of the thyroid gland. The prevalence of the pyramidal lobe in thyroid glands and its features have been studied in autopsy series but there is little information regarding its parameters in patients or normal subjects. The purpose of the current study was to assess the frequency, location, and size of the pyramidal lobe using computed tomography (CT) of the neck.

From January to December 2010, 327 patients who underwent neck CT for trauma, thyroid cancer, pharyngolaryngeal malignancy, a palpable neck mass, cervical lymphadenopathy, and vocal cord paralysis were enrolled in the study. Their neck CTs were retrospectively analyzed by a single radiologist. Small pyramidal lobes (<9 mm) were not included in the study.

A pyramidal lobe was present in 41.3% (135/327) of the patients; some pyramidal lobes showed complete separation from the thyroid gland (12.6%, 17/135). There was no difference in the frequency of pyramidal lobe detection by gender (p>0.05, Fisher's exact test). The pyramidal lobe predominantly originated from the left thyroid gland in 54.1% (73/135) of patients. There were two patients in whom the pyramidal lobe was located bilaterally (one case from both the right and left sides of the thyroid gland and one case from the left side and midline of the thyroid gland). The average length and volume of the pyramidal lobes were 25.0 mm and 129.4 mm(3), respectively. The upper margin of the pyramidal lobe was most commonly located at the level of the thyroid cartilage.

The prevalence of the pyramidal lobe in the left lobe of the thyroid gland is somewhat greater than 50% using the criteria employed in this study. Neck CT is useful for detecting the presence, size, configuration, and location of the pyramidal lobe.