title: Pyramidal lobe of the thyroid gland and the thyroglossal duct remnant: a study using human fetal sections.
abstract: To investigate developmental changes in the thyroglossal duct, we observed serial sagittal sections of eight embryos (crown-rump length (CRL) 6-12 mm; approximately 5-6 weeks of gestation) as well as serial horizontal or cross-sections of 70 embryos and fetuses (CRL 15-110 mm; 6-15 weeks). In the sagittal sections, the thyroglossal duct was identified as a small sheet or mass of relatively large cells with vacuolization anterior, superior or inferior to the fourth pharyngeal arch artery. However, we found no continuous duct-like structure that reached the thyroid gland. Thus, previous classical schemes might have overestimated the continuity of the duct. Among cross-sections of 70 specimens, we found the thyroglossal duct remnant in only two specimens (CRL 15 mm and 100 mm), in contrast to the pyramidal lobe, which was seen in one-third of the specimens. The duct remnant ran downward along the lateral edge of the hyoid body to reach the anterior aspect of the thyroid cartilage. However, the connection between the pyramidal lobe and the duct remnant was interrupted by the anterior cervical muscles. Therefore, it was unlikely that the thyroglossal duct remnant would more frequently be evident in fetuses than in adults. The highly tortuous course of the duct along the lingual aspect of the hyoid body, which has been reported previously, appeared to become established near term. Descent of the thyroid gland was not evident after the CRL 20 mm stage (6 weeks): the gland appeared to retain its position at the level of the third-sixth cervical vertebrae.
authors.affiliation: Department of Otolaryngology and Head and Neck Surgery, Tohoku University Graduate School of Medicine, Sendai, Japan. Electronic address: y-takanashi@mti.biglobe.ne.jp.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Takanashi
authors.affiliation: Department of Otolaryngology and Head and Neck Surgery, Tohoku University Graduate School of Medicine, Sendai, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Honkura
authors.affiliation: Institute of Embryology, Universidad Complutense, Madrid, Spain.
authors.forename: Jose Francisco
authors.initials: JF
authors.lastname: Rodriguez-Vazquez
authors.affiliation: Division of Internal Medicine, Iwamizawa Kojin-kai Hospital, Iwamizawa, Japan.
authors.forename: Gen
authors.initials: G
authors.lastname: Murakami
authors.affiliation: Department of Otolaryngology and Head and Neck Surgery, Tohoku University Graduate School of Medicine, Sendai, Japan; Laboratory of Rehabilitative Auditory Science, Tohoku University Graduate School of Biomedical Engineering, Sendai, Japan.
authors.forename: Tetsuaki
authors.initials: T
authors.lastname: Kawase
authors.affiliation: Department of Otolaryngology and Head and Neck Surgery, Tohoku University Graduate School of Medicine, Sendai, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Katori
mesh_terms: D005333:Fetus / Q000033:anatomy & histology*; D005865:Gestational Age; D006801:Humans; D013955:Thyroglossal Cyst / Q000196:embryology*; D013961:Thyroid Gland / Q000196:embryology* / Q000601:surgery
keywords: Development; Human embryo; Pyramidal lobe; Thyroglossal duct; Thyroid gland