The pyramidal lobe: clinical anatomy and its importance in thyroid surgery.

The pyramidal lobe could be a source of pitfalls in thyroidectomy, due to its frequency but unreliable preoperative diagnosis on scintigraphic images. Special attention has to be paid to the pyramidal lobe to avoid leavings of residual tissue when complete removal of the thyroid is indicated. Sixty cadaveric specimens were examined with special emphasis to the topographical anatomy and expansion of the pyramidal lobe. A pyramidal lobe was found to be present in 55% of the cadavers (32/58). It was found more frequently in men than in women. In men the median length was 14 mm and in women 29 mm. An accessory thyroid gland was present in one specimen, in four cases the isthmus was missing. The pyramidal lobe branched off more frequently from the left part of the isthmus (16) than from the right (7) or the midline (9). In two cases it originated from the left lobe. Additionally 23 scintigraphic images were analyzed to evaluate the visualization of a pyramidal lobe. Only three of them showed enlargements of the isthmus that could be taken as a pyramidal lobe. Due to its frequency the pyramidal lobe should be regarded as a normal component of the thyroid. It is not reliably diagnosed by scintigraphic imaging because scintigraphy can only give functional information but not morphological one. Therefore the anterior cervical region has to be investigated very carefully during operation in order not to leave residual thyroid tissue in total thyroidectomy.