Thyroid Research and Practice

ORIGINAL ARTICLE
Year
: 2014  |  Volume : 11  |  Issue : 2  |  Page : 49--54

Postoperative hypothyroidism after thyroidectomy for nontoxic multinodular goiter: Can we prevent it by leaving more?


Badamutlang Dympep1, Arun Kumar Kakar1, Raman Tanwar1, Ravi L Shankar2, Ishita B Sen3, Ethel Shangne Belho3,  
1 Department of General Surgery, Maulana Azad Medical College and Lok Nayak Hospital, New Delhi, India
2 Department of Nuclear Medicine and Thyroid Consultant, Department of Nuclear Medicine, Institute of Nuclear Medicine and Allied Sciences, Timarpur, New Delhi, India
3 Department of Nuclear Medicine. Sir Ganga Ram Hospital, New Delhi, India

Correspondence Address:
Raman Tanwar
1013, Sector 15, part 2, Gurgaon 122 001, Haryana
India

Abstract

Introduction: A study was done to evaluate the function of the thyroid remnant after subtotal and near total thyroidectomy (STT and NTT) in nontoxic multinodular goiter (MNG) by using radioactive iodine uptake (RAIU) and serum thyroid stimulating hormone (TSH), after leaving variable amounts of remnant thyroid tissue. Materials and Methods: A prospective study included 25 patients with nontoxic MNG over a period of 18 months where in STT and NTT was performed. Depending on the availability of the normal thyroid tissue found intraoperatively, a definite volume of thyroid tissue was left in the tracheoesophageal groove along the recurrent laryngeal nerve. Serum TSH and RAIU were performed 4 weeks after surgery. Patients were divided into three groups A, B, and C depending on the size of thyroid remnant left during surgery that is a volume of <2, 2-5, and >5 mL, respectively. Results: There is no statistical significant correlation seen between the size of the remnant thyroid tissue, hypothyroidism, and the postoperative serum TSH value. RAIU study conducted at 4 weeks postsurgery showed no correlation between the volume of the thyroid tissue remnant and its RAIU uptake. Conclusion: The thyroid function of the patients after thyroidectomy does not depend on the volume of the thyroid remnant left. There may be many other factors which determine the thyroid function like the total preoperative gland mass, histopathological nature of the gland, sex, and preoperative thyroid function.



How to cite this article:
Dympep B, Kakar AK, Tanwar R, Shankar RL, Sen IB, Belho ES. Postoperative hypothyroidism after thyroidectomy for nontoxic multinodular goiter: Can we prevent it by leaving more?.Thyroid Res Pract 2014;11:49-54


How to cite this URL:
Dympep B, Kakar AK, Tanwar R, Shankar RL, Sen IB, Belho ES. Postoperative hypothyroidism after thyroidectomy for nontoxic multinodular goiter: Can we prevent it by leaving more?. Thyroid Res Pract [serial online] 2014 [cited 2019 Aug 20 ];11:49-54
Available from: http://www.thetrp.net/text.asp?2014/11/2/49/129724


Full Text

 Introduction



Thyroidectomy is one of the most common operations performed for patients with nontoxic multinodular goiter (MNG). In recent years, total thyroidectomy has emerged as a more acceptable surgical option to treat patients with nontoxic MNG. [1],[2],[3] The goal of this procedure is to minimize the risk of reoperation for incidental thyroid carcinoma in MNG and the incidence of recurrent laryngeal nerve injury. The incidence of thyroid cancer varies from 7.5 to 13% in cases of nontoxic MNG [4],[5],[6] and is one of the major factors, due to which surgeons are now favoring total thyroid removal. In such a scenario it is valuable to know, what minimum amount of gland can help prevent postoperative hypothyroidism such that the need for thyroid medication is avoided.

The aim of a surgeon performing subtotal and near total thyroidectomy (STT and NTT) for MNG is to try to keep the patient euthyroid postoperatively avoiding the need for lifelong thyroid replacement. The long-term risks of hypothyroidism after subtotal resection of nontoxic MNG is not sufficiently described, but it is probably not significantly different from the 10-20% incidence reported for toxic MNGs. [7] The remnant size is extremely important in determining the postoperative thyroid functional status in toxic goiter. Its importance in euthyroid goiters cannot be overruled. The quantification of the thyroid remnant size has been a subject of great interest. Till today there is no satisfactory method of estimating the thyroid remnant intraoperatively. In this regard, the surgeon has often to depend on his visual and tactile perceptions. The estimation of the thyroid remnant size per operative has been performed with different cumbersome and crude methods usually with substantial errors. The remnant size has been determined by using callipers, moulds, comparing the resected specimen with the thyroid remnant, or by measuring the specific gravity. [8],[9]

Lundstorm and Gillquist [10] in 1981 found that after thyroid surgery, patients developing hypothyroidism could be picked up within the first 4-6 weeks by demonstrating increased thyroid stimulating hormone (TSH) levels, whereas patients who did not develop hypothyroidism even as late as 5 years after surgery had normal serum TSH levels in the early postoperative period, that is, 4-6 weeks after surgery.

The role of using radioiodine uptake studies in the determination of the thyroid functional status post STT and NTT has not been ventured by many. A thyroid uptake study provides quantitative information regarding the percent of the administered activity taken up by the thyroid gland. The most common clinical indication for a percentage radioactive iodine uptake (% RAIU) study is to aid in the differential diagnosis of newly diagnosed thyrotoxicosis. Other indications being in Grave's disease for estimating the dose of I-131 therapy; in thyroid cancer follow-up for recurrence and also for estimating the function of the thyroid remnant postsurgery. [11]

Presently the endocrine surgeon faces the dilemma of how much of the gland to leave to render the patient euthyroid after thyroidectomy. Both subjective and objective assessment intraoperatively may have a doubtful functional correlation with postoperative thyroid function.

 Materials and Methods



A prospective study was conducted in the Department of Surgery, Maulana Azad Medical College and associated Lok Nayak Hospital, New Delhi in association with Thyroid Clinic, Institute of Nuclear Medicine and Allied Sciences (INMAS), Timarpur, Delhi in which 25 patients underwent thyroid surgery for MNG over a period of 18 months. All patients presenting with bilobar thyroid enlargement and a euthyroid status were taken up for surgery. Patients with thyroid malignancy, single thyroid nodule requiring hemithyroidectomy, pregnancy, recurrence, thyroiditis, or toxic MNG were excluded from the study. None of the patients had previously been treated with radioiodine therapy or external irradiation to the neck nor were taking any medication known to affect RAIU.

The patients were divided into three groups: Group A having a remnant thyroid volumes of less than 2 mL; Group B of 2-5 mL; and Group C of more than 5 mL. The main indications for surgery were the presence of large goiter with compressive effect and cosmesis.

The study plan was reviewed and approved by our institutional ethics committee, and informed consent was obtained from all patients.

NTT was performed by the capsular dissection method, leaving less than 2 g (2 mL) of thyroid tissue in close proximity to the recurrent laryngeal nerve and parathyroid glands. Cases in which a dominant nodule was present underwent lobectomy of the lobe containing the dominant nodule and near total resection of the contralateral lobe was added. In all patients with multiple nodules but no dominant nodule, bilateral NTT was performed. STT was performed either by the Hartley-Dunhill's procedure or bilateral STT, leaving approximately 4-5 g of remnant thyroid tissue.

Preoperative estimation of volume of the thyroid gland by ultrasonography

Preoperative estimation of the volume of the thyroid gland was done within 7 days before the proposed day of surgery by the ultrasound, using transducer of 7.5-10 MHz, and grey scale sector scanner. Patients were examined in the supine position with the neck hyper extended. The volume of individual discrete/solid/mixed/cystic areas was taken into account. The total volume of the thyroid gland was taken as the sum of the volume of the bilateral lobes and the isthmus.

The volume was calculated by using the ovoid formula where:

V =π/6 × length × breadth × thickness.

Intraoperative volume determination of excised thyroid gland

Immediately after operation, the volume of thyroid glands removed in vivo was measured by volume displacement method (Archimedes' principle) using measuring glass cylinder.

By using metal calipers, the accurate dimensions of the remnant thyroid gland were measured accordingly.

The volume of the remnant size was then calculated using the formula of the ovoid.

V = π/6 × length × breadth × thickness.

Evaluation of remnant thyroid function

All the patients who underwent surgery for MNG were not put on any thyroid drugs supplement in the immediate postoperative period. The thyroid function of the patients was determined by serum level at 4 weeks postsurgery. Assessment of 24-h RAIU was performed after oral administration of a capsule containing 25 micro Ci of iodine-131. Iodine-131 was supplied by the Board of Radio Isotope Technology (BRIT), Mumbai, India. RAIU was determined by the Thyroid Uptake System-Atom Lab 950. The %RAIU increased progressively over 24 h. The normal range taken for the 2-6 h% RAIU was 4-15% and the normal range for the 24 h%RAIU was 15-35% (INMAS, Timarpur).

Data were analyzed using the Statistical Package for the Social Sciences software for Windows (SPSS) version 16.0 software for windows. Results with normal distribution and non-Gaussian distribution were expressed as mean ± standard deviation (SD) and median value, respectively. Correlation analyses were performed using nonparametric Spearman's correlation and two-way analysis of variance (ANOVA) tests. Results were considered statistically significant when the two-tailed P was less than 0.05.

 Results



A total of 43 patients were operated during the period of study over 18 months in our institute. Of these 25 patients were included in the study on the basis of inclusion and exclusion criteria. The 25 patients who underwent surgery for MNG were aged 44.16 ± 12.45 years (mean ± SD, range = 22-68 years). The percentage of female was 92% and male was 8%. The distribution of patients is as shown in [Table 1] (diagnosis was based on final histopathological report).{Table 1}

All the 25 patients underwent surgery for MNG and only those patients who were euthyroid were included in this study. The patients were subjected to NTT or STT, depending on the intraoperative findings of six and 19 patients each.

The preoperative serum levels of TSH and free thyroxine (T4) were 2.74 ± 1.27 mIU/L and 1.21 ± 0.26 ng/dL, respectively. During the 1 st postoperative month, the mean remnant thyroid volume, the mean serum TSH, and the mean RAIU % at 24 h were 3.97 ± 2.22 mL, 43.77 ± 37.11 mIU/L, and 16.21 ± 8.62%, respectively. The preoperative volume of the thyroid gland resected and the remnant thyroid tissue left behind were calculated as described in the methodology. In [Table 2], findings of the operated cases with the type of surgery, the intraoperative findings, the volume of the thyroid gland resected, and the remnant thyroid tissue left behind have been tabulated. There was no operative mortality or other complications like hypoparathyroidism or recurrent laryngeal nerve palsy.{Table 2}

All the patients who had undergone surgery either by NTT or STT were subjected to measurement of thyroid function by the serum TSH level, 4 weeks after surgery. We correlated the size of the thyroid remnant left in situ during the surgery with the thyroid function after a postoperative period of 4 weeks.

All the patients who had undergone surgery were subjected to RAIU study 4 weeks postsurgery. This was done to measure the function of the remnant thyroid gland. In our setup the normal RAIU is taken as the 24 h uptake and with normal range of 15-35%.

Patient evaluation by remnant thyroid volume

There was no significant change in the RAIU observed when the remnant thyroid volume was increased. The serum TSH level, however, decreased in group C with a volume of >5 mL. The median remnant thyroid tissue RAIUs of Groups A, B, and C were 24, 17.6, and 18% at 24 h. Taking the RAIU to be 15-35% as a normal range for this population, it was seen that all the groups had a normal uptake but there was no increase in the uptake with increase in the size of the thyroid remnant left after surgery. The mean, median, and SD of the TSH and RAIU of Groups A, B, and C are shown in [Table 3] and [Table 4].{Table 3}{Table 4}

Nonparametric correlation analysis revealed that remnant thyroid volume was not significantly and positively correlated with remnant thyroid tissue RAIU. There was a negative correlation between the remnant thyroid volume and the postoperative serum TSH level (R 2 = −0.36, P < 0.0001), also there was no significant correlation between the remnant thyroid volume and the RAIU also (R 2 = 0.0754) and between the remnant thyroid tissue RAIU and the postoperative serum TSH level (R 2 = 0.6919, P < 0.0001) [Figure 1], [Figure 2], [Figure 3].{Figure 1}{Figure 2}{Figure 3}

 Discussion



It is often speculated that the size of the thyroid remnant must play an important part in determining the functional result but the assessment is often unreliable. When a subjective assessment is done, this leads to a great variation in remnant size. However, the quantification of the remnant has lately been a subject of rising interest as more patients have been found to develop biochemical signs of hypothyroidism after surgery. It has been suggested that patients with small remnants (<4.2 mL) [12] are more liable to develop a subclinical hypothyroidism after surgery than patients with large remnants (>4.20 mL). [9],[12],[13]

The estimation of remnant size has been performed with different methods, usually with substantial error. [9],[14] Review of the literature shows that the most significant etiological factor in postoperative hypothyroidism is small remnant size. While the incidence of hypothyroidism in a patient is closely associated with remnant size, other factors such as antithyroglobulin antibodies, histopathological nature of the disease, age, sex, type of surgery, blood group, etc., may also influence the outcome in this regard. Some authors have expressed the view that there is an optimum remnant size which in their centers is associated with a low incidence of hypothyroidism. [12],[15],[16]

Lundstorms and Gillquist [10] found that after thyroid surgery, patients developing hypothyroidism can be picked up within the first 4-6 weeks by demonstrating increased serum TSH levels, whereas patients who do not develop hypothyroidism even as late as 5 years after surgery had normal serum TSH levels in the early postoperative period, that is, 4-6 weeks after surgery. Therefore, in the present study, thyroid function was done 4-6 weeks after surgery to pick up patients having deranged thyroid function following surgery.

Lundstrφm and Norrby (1980) [17] reported the incidence of raised serum TSH levels as 36 and 50%, respectively with the remnant size of >8.1 g and <8.0 g. This statistically significant fact emphasizes the need for leaving behind thyroid tissue more than 8.22 ± 1.06 mL or 0.17 ± 0.01 mL/kg body weight to prevent postoperative occult or overt hypothyroidism in cases of nontoxic goiters.

Young and Macleod in 1972 [9] studied the fate and function of the thyroid remnant by clinical, RAIU, and scan studies. Remnant size did not appear to be critical, but hypo function was not found to occur over 8 cc. Above this size of residuum, hypothyroidism did not appear to be directly due to the operation per se and was not regarded as postoperative.

Fawzy et al., [12] in 2006, evaluated the thyroid function of 119 patients at 6 months post STT for MNG including both euthyroid and hyperthyroid status. A strong negative correlation (R = −0.79) was reported between the thyroid remnant volume and the TSH level. Euthyroid patients had a mean volume of thyroid tissue (4.31 ± 0.88 mL) significantly (P < 0.01) higher than that of hypothyroid patients (2.16 ± 1.25 mL). In this study, STT led to hypothyroidism in 71% patients. They concluded that the theoretical minimal volume of remnant thyroid tissue required to avoid hypothyroidism was 4.20 mL.

From the literature mentioned above it is seen that the volume of the thyroid tissue remnant plays an important role in determining the thyroid function. In the present study, an attempt was made to find out the correlation between the thyroid remnant size and postoperative thyroid function in euthyroid goiters. It was seen that all the patients who had underwent surgery (NTT/STT) for MNG developed hypothyroidism 4 weeks postoperatively. The minimum value of serum TSH level was 10.20 mIU/L which was seen in two cases where the remnant volume was 3.26 and 6.20 mL; and the maximum value of serum TSH was 151.90 mIU/L, which was seen in the remnant volume of 5.24 mL. The range of the thyroid remnant volume was 0.85 mL (corresponding TSH = 13.60 mIU/L) to 9.60 mL (corresponding TSH = 14.21 mIU/L). Hence, all the patients developed hypothyroidism and there is no statistically significant correlation seen between the remnant thyroid volume and the postoperative serum TSH value.

Erbil et al., [18] studied the function of the thyroid remnant by using ultrasonography, serum TSH, and RAIU in MNGs. In their study, 66 patients were divided into two groups according to their functional status, that is, those operated upon for nontoxic MNG (group one) and those operated upon for hyperthyroidism (group two). Ultrasonography, RAIU, and TSH assay were performed in all patients during the 1 st postoperative month. The two groups were subdivided according to the amount of remnant thyroid volume detected on ultrasonography into those with a volume of 2, 2-5, and >5 mL. The remnant thyroid volume was positively correlated with the RAIU (r s = 0.684, P = 0.0001). The increase in remnant thyroid tissue RAIU was significantly greater in the patients operated upon for hyperthyroidism compared with those operated upon for nontoxic MNG (P = 0.0001). There was a negative correlation between remnant thyroid volume and postoperative serum TSH level (r s = 20.865, P = 0.0001) and between remnant thyroid tissue RAIU and postoperative serum TSH level (r s = 20.682, P = 0.0001).

RAIU study of the remnant thyroid tissue was also conducted at 4 weeks postsurgery. There was no correlation seen between the volume of the thyroid tissue remnant and its RAIU uptake. The thyroid tissue that was left behind might not have been fully functional. There are no methods at present for measuring the functional volume of the thyroid gland in vivo.

In the present study, STT and NTT for benign MNG led to a 100% hypothyroidism rate. The other factors on which the function of the remnant thyroid tissue depends are the total preoperative gland mass, [19],[20] histopathological nature of the gland, sex, and preoperative thyroid function. [18],[21] The smaller the remnant volume, the higher is the risk of hypothyroidism occurrence. Our country is an area endemic for goiters and very often patients present with a highly distorted structure of thyroid gland in which it is not always possible for the surgeon to find a healthy portion of thyroid tissue to preserve. The aim of performing STT for MNG is to keep the patients euthyroid postoperatively, avoiding the need for lifelong thyroid replacement. Our results show that even with a remnant of adequate size (>5.1 mL), preservation of normal thyroid function is not warranted and the risk of hypothyroidism remains high.

Since the study consisted of a small number of 25 patients with the male to female ratio of 2:23, no statistical significant conclusions can be drawn regarding the influence of sex and age on the function of the thyroid gland remnant postsurgery in benign MNG.

 Conclusion



From this study, it can be concluded that the thyroid function of the patients postsurgery does not depend on the size of the remnant. There is no statistically significant correlation between the remnant size and its radioiodine uptake or TSH values. Hence, the size of the thyroid remnant left in STT or NTTs for MNG is not an important factor in determining the thyroid function postsurgery.

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