Pyramidal lobe of the human thyroid gland: an anatomical study with clinical implications.

The presence, position, extent, relationships to neighboring structures and size of the human pyramidal lobe were investigated in 58 human post-mortem specimens in order to determine the variability of this structure. The pyramidal lobe is found in 55.2% of cases as a single conical extension of the thyroid gland. It was present more often in male (53.1%) than in female (46.9%) specimens and located slightly more often on the left side of the midsagittal plane (53.1%). According to the origin and location of its base, we defined five types of pyramidal lobe, with the left-sided types (Types III and IV) being predominant. The pyramidal lobe was 22.6 mm long, 11.2 mm wide and 3.6 mm thick (mean values). The means of all measured parameters were higher in female than in male specimens (pyramidal lobe was 2.3 mm longer, 1.6 mm wider and 0.4 mm thicker in female specimens) but these differences were not significant. In addition, we found that the size of the pyramidal lobe was dependent on the presence of a fibrous or muscular band that may represent a fibrous remnant of the thyroglossal duct or the levator glandulae thyroideae muscle. The pyramidal lobe was four times longer and its base was two and a half times wider and three times thicker when it was associated with this band. We believe that our data can be used to perform safer and more effective partial thyroidectomy in order to preserve thyroid function after surgical treatment.