Isthmus-preserving total bilobectomy: an adequate operation for C-cell hyperplasia

Autopsy studies show that C cells deriving from the ultimobranchial body and migrating into the thyroid do not reach the isthmus region and are distributed along the vertical axes of thyroid lobes. This was confirmed in a surgical series of 58 patients (34 with preoperatively normal and 24 with elevated serum calcitonin) where no calcitonin-positive cells were demonstrable immunohistochemically within separately investigated isthmi. Consequently, isthmus-preserving total bilateral lobectomy (IPTB) may be regarded as an adequate surgical procedure for C-cell hyperplasia (CCH).

IPTB was performed from October 2001 to December 2004 in 64 patients, 59 patients with nodular goiter and slightly to moderately elevated serum calcitonin (stimulated under 500 pg/ml) (group A, apparently sporadic cases) and in 5 patients undergoing prophylactic surgery for hereditary medullary thyroid carcinoma (MTC) with intermediate- or low-risk RET mutations (non-634) (group B). The surgical procedure focused on meticulous total extracapsular resection of both thyroid lobes, preservation of an isthmus remnant of about 3 ml (smaller in children), and histologic workup of the border zones of resection in addition to that of the completely removed lobes. When malignancy could be proven intraoperatively (7 patients) or when the isthmus turned out to contain nodular lesions (4 patients), completion total thyroidectomy (plus lymphadenectomy) was performed as a one-stage procedure. Second-stage total thyroidectomy was performed in 3 cases. Thus, IPTB was the definitive surgical procedure in 50 patients (45 of group A and all 5 of group B).

In all of the 50 definite IPTB cases, postoperative serum calcitonin was below the measurable limit (2 pg/ml); stimulated calcitonin was below the measurable limit in 47 (including all of group B) and was measurable in 3 sporadic cases in a lower-normal range between 2.4 and 3.5 pg/ml. Genetic screening of the apparently sporadic cases with CCH was positive in one (codon 791). The risk of recurrent laryngeal nerve paralysis seems not to be elevated (0% permanent); permanent hypocalcemia occurred in 1 patient (2%). Follow-up data of 37 patients, median 18 (6-36) months, showed continuously nonmeasurable serum calcitonin with one exception, where it was in the normal range after 18 months. All IPTB patients are still under substitution therapy with L-thyroxine (median 125 mug/day) with decreasing tendency in all 3 children after prophylactic operation, the latter also showing an increasing volume of well-vascularized isthmi (from 1.5 to 2.5 ml).

IPTB reliably removes all C cells. There may not be need for total thyroidectomy (TTx) in cases with CCH. When necessary, completion TTx can be performed easily without additional risk. IPTB leaves a functionally relevant remnant, corresponding to that of a subtotal resection. This might be of importance especially for prophylactic surgery in children where the isthmus can compensate for the loss of thyroid function with time.