The importance of pyramidal lobe in thyroid surgery.

INTRODUCTION Pyramidal lobe (PL) is an embryological remnant of the thyro-glossal duct; its incidence varies from 15% to 75% but data concerning its size are lacking and limited to autoptic and radiologic evidences. Aim of our study is to elucidate the intraoperative frequency, location and surgical management of the PL. PATIENTS AND METHODS 604 total thyroidectomy were performed between 1999 and 2007 in Unit of General and Thoracic Surgery of the University Policlinico of Palermo. The intraoperative incidence of PL was 12% (57% male, 43% female, mean age 42.5 years), but only about 50% were identified preoperatively with ultrasonography (US) (4% false positive) or with Tc-99m pertechnetate scintigraphy (8% false positive). RESULTS In 77% of cases the lobe was affected by nodular pathology in multinodular goiter, in 1.3% by papillary cancer; in the rest of cases was normal. PL branched off more frequently from the left part of the isthmus (96%) than from the right part (4%) and in 25% of cases was associated with delphian lymph node. No PL exceeded 2 cm in length in pathologic specimen. There was no difference in thyroidectomy operative time with or without PL. At US, scintigraphic and laboratory follow-up (2 months-8 years), no incomplete resection of the gland due to the presence of PL were recorded. DISCUSSION In anatomical studies the frequency of the PL is between 15% and 75%; PL is in 10-17% of normal subject and in 43% of patients with multinodular goiter. The PL is of great importance to the thyroid surgeon during thyroidectomy: it is crucial to look for, identify, and remove the PL, as this can be a cause of incomplete resection of the gland. If left behind in a patient who will require postoperative radioactive iodine, its presence will virtually nullify the anticipated benefit of I131 by absorbing most of the radioactive material; may exist relapse of cancer from PL left in situ. CONCLUSIONS The intraoperative frequence of PL is 12%, and it is considered a normal component of the thyroid. Scintigraphic visualization of the PL depends on the kind of thyroid disorder and on the experience of radiologist, so the PL can often not be diagnosed by scintigraphic imaging. Finally, the whole anterior cervical region has to be investigated very carefully during thyropidectomy not to overlook a long or thin pyramidal lobe or other ectopic thyroid tissue because actually doesn't exist the goldstandard preoperative method to diagnoses PL.