The Prevalence and Features of Thyroid Pyramidal Lobe, Accessory Thyroid, and Ectopic Thyroid as Assessed by Computed Tomography: A Multicenter Study

Abstract

Background and Purpose: Understanding the computed tomography (CT) characteristics of the pyramidal lobe and other thyroid variations and detecting them accurately using preoperative neck CT will minimize unnecessary remnant thyroid tissue after total thyroidectomy in patients with thyroid cancer. The purpose of the present study was to assess the frequency, location, and size of the pyramidal lobe and other thyroid variations using a large-scaled, multicenter study. Methods: Neck CT scans for 200 patients were selected from 11 institutions; a total of 2200 patients were included in the study. The patients underwent neck CT for the following reasons: trauma, known thyroid malignancy, cervical lymphadenopathy, palpable neck mass, oropharyngolaryngeal malignancy, vocal cord palsy, postchemotherapy CT follow-up, inflammatory or infectious neck lesion, parathyroid abnormality, and patient request. A single radiologist at each institution retrospectively analyzed 200 neck CT scans. Each radiologist investigated the presence, location, length, volume, and upper end of the pyramidal lobe and its separation or continuity with the main thyroid gland as well as the presence, location, length, and volume of the accessory or ectopic thyroid using a picture archiving and communication system. Results: A pyramidal lobe was present in 44.6% (981/2200) of the patients. The prevalence for the pyramidal lobe at the participating institutions ranged from 28.0% to 55.0% (mean, 44.6%). Pyramidal lobes originating from the left side of the thyroid were most common, and the number of pyramidal lobes showing separation from the main thyroid gland was 90 (9.2%). The mean anteroposterior diameter, transverse diameter, and length of the pyramidal lobe were 2.3, 5.9, and 20.8 mm, respectively. Among both men and women, the most common level of the upper end of the pyramidal lobes was the thyroid cartilage, but there was a significant difference in the frequency of the pyramidal lobe between males and females (p < 0.0001). The rate of the pyramidal lobe detection in the 2-mm-slice-thickness group was higher than those in the 2.5- and 3-mm groups (p = 0.0003). Conclusion: Neck CT is useful for detecting the presence, size, configuration, and location of the pyramidal lobe and other thyroid variations.