**2. Classification of the IPTG**

1. According to the location relationship between the IPTG and thymus, four groups were classified by J. Grisoli in 1979 [8]. Group 1: the parathyroid gland in the usual classic position, in contact with the terminal branches of the inferior thyroid artery, behind or below the inferior poles of the thyroid lobes (65% of cases); Group 2: the parathyroid gland in a thyrothymic position, more or less equidistant from the inferior thyroid lobe and the thymic cornu (17.5% of cases); Group 3: the superior thymic parathyroid gland, situated in the cornua of the thymus or their immediate vicinity (15.5% of cases); Group 4: intrathymic parathyroid (2% of cases) (**Figure 1**).

**Figure 1.** Position of inferior parathyroid gland (by J Grisoli). (A) Usual position; (B) thyro-thymic position; (C) superior

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**Figure 2.** The three main types of parathyroid gland (by GS Wu). Type A, nonattachment to the thyroid and has adequate blood supply; type B1, attached lightly to the thyroid and retains adequate blood supply after thyroid removal; type B2, attached tightly to the thyroid and changes color easily, in which case, the distal tissue is cut in half for autograft; type B3, blood supply is derived mostly from the thyroid gland and may be treated as either type B2 or type C according to the surgeon's skill; type C, under cover of the thyroid capsule and can only be preserved by total auto-transplantation.

thymic position; (D) intrathymic.

**2.** Based on the relationship between the parathyroid gland and the thyroid gland as well as the color change in the parathyroid glands after separation from the thyroid, different categories of parathyroid gland are as follows [9]:

Type A, no dependency on the thyroid, and with adequate blood supply and no color change after thyroidectomy; B1, partial blood supply from the thyroid but retains adequate blood supply after removal of the thyroid; B2, partial blood supply from the thyroid and becomes devascularized after the removal of the thyroid; B3, blood supply mostly from the thyroid; difficult to preserve in situ and C, blood supply completely dependent on the thyroid. The classifications were used to decide between in situ preservation and auto-transplantation (**Figure 2**).

**3.** According to the positional relationship between IPTG and the thyroid gland, JQ Zhu classified IPTG into two types [10], namely type A (close contact) and type B (non-close contact). Type A includes A1 (planar attachment), A2 (embedded attachment), and A3 (intra-thyroid); type B includes B1 (around thyroid), B2 (intra-thymus), and B3 (blood supply from thymus or mediastinum) (**Figures 3** and **4**)

During TT and CND, IPTG typically undergoes "dissection" twice. At first instance, the IPTG is exposed and preserved by meticulous capsular dissection during thyroid lobectomy; at second instance, the IPTG is identified and preserved in situ while the central neck fibro-fatty tissue with lymph nodes is removed. The first instance is the premise and basis of the second instance, because in situ preservation of IPTG in CND becomes impossible if IPTG has been devascularized or resected during thyroid lobectomy. The identification and preservation of IPTG in the first instance of dissection facilitates the preservation of the IPTG in situ in CND Inferior Parathyroid Gland Preservation In Situ during Central Neck Dissection for Thyroid… http://dx.doi.org/10.5772/intechopen.78636 19

Hypoparathyroidism is the most common and a potentially serious complication of thyroid surgery, which can lead to metabolic and physiologic disturbance, prolonged hospitalization and medical supplementation [3–6]. In general, the prevalence of transient and permanent hypoparathyroidism is reported to range from 14–60% and 4–11%, respectively [7]. Total thyroidectomy (TT) with central neck dissection (CND) significantly increases the rate of transient and permanent hypoparathyroidism in comparison with total thyroidectomy.

In this chapter, a new operation concept, "a layer of thymus-blood vessel-inferior parathyroid gland (TBP)," is mainly introduced to preserve the inferior parathyroid gland (IPTG) *in situ*

1. According to the location relationship between the IPTG and thymus, four groups were classified by J. Grisoli in 1979 [8]. Group 1: the parathyroid gland in the usual classic position, in contact with the terminal branches of the inferior thyroid artery, behind or below the inferior poles of the thyroid lobes (65% of cases); Group 2: the parathyroid gland in a thyrothymic position, more or less equidistant from the inferior thyroid lobe and the thymic cornu (17.5% of cases); Group 3: the superior thymic parathyroid gland, situated in the cornua of the thymus or their immediate vicinity (15.5% of cases); Group 4: intrathymic

**2.** Based on the relationship between the parathyroid gland and the thyroid gland as well as the color change in the parathyroid glands after separation from the thyroid, different

Type A, no dependency on the thyroid, and with adequate blood supply and no color change after thyroidectomy; B1, partial blood supply from the thyroid but retains adequate blood supply after removal of the thyroid; B2, partial blood supply from the thyroid and becomes devascularized after the removal of the thyroid; B3, blood supply mostly from the thyroid; difficult to preserve in situ and C, blood supply completely dependent on the thyroid. The classifications were used to decide between in situ preservation and auto-transplantation (**Figure 2**).

**3.** According to the positional relationship between IPTG and the thyroid gland, JQ Zhu classified IPTG into two types [10], namely type A (close contact) and type B (non-close contact). Type A includes A1 (planar attachment), A2 (embedded attachment), and A3 (intra-thyroid); type B includes B1 (around thyroid), B2 (intra-thymus), and B3 (blood sup-

During TT and CND, IPTG typically undergoes "dissection" twice. At first instance, the IPTG is exposed and preserved by meticulous capsular dissection during thyroid lobectomy; at second instance, the IPTG is identified and preserved in situ while the central neck fibro-fatty tissue with lymph nodes is removed. The first instance is the premise and basis of the second instance, because in situ preservation of IPTG in CND becomes impossible if IPTG has been devascularized or resected during thyroid lobectomy. The identification and preservation of IPTG in the first instance of dissection facilitates the preservation of the IPTG in situ in CND

during CND for papillary thyroid carcinoma (PTC).

**2. Classification of the IPTG**

18 Thyroid Disorders

parathyroid (2% of cases) (**Figure 1**).

categories of parathyroid gland are as follows [9]:

ply from thymus or mediastinum) (**Figures 3** and **4**)

**Figure 1.** Position of inferior parathyroid gland (by J Grisoli). (A) Usual position; (B) thyro-thymic position; (C) superior thymic position; (D) intrathymic.

**Figure 2.** The three main types of parathyroid gland (by GS Wu). Type A, nonattachment to the thyroid and has adequate blood supply; type B1, attached lightly to the thyroid and retains adequate blood supply after thyroid removal; type B2, attached tightly to the thyroid and changes color easily, in which case, the distal tissue is cut in half for autograft; type B3, blood supply is derived mostly from the thyroid gland and may be treated as either type B2 or type C according to the surgeon's skill; type C, under cover of the thyroid capsule and can only be preserved by total auto-transplantation.

in situ preservation of the IPTG in CND could be very difficult. This can be attributed to the fact that IPTGs assume a more variable position in the adult neck, thus making their detection difficult. Moreover, IPTGs are located in the area of central neck lymph node dissection and

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How to preserve the IPTG during the thyroid lobectomy, a concept "meticulous capsular dissection" was put forward by NW Thompson in 1973 [11], and further explanation was given by Attie and other scholars [12]. The protection of the parathyroid glands and to the recurrent laryngeal nerve is achieved by using capsular dissection, hugging the gland and dividing the tertiary branches (i.e., the third order of division) of the vessels while dissecting the parathyroid glands with their vascular pedicles free from the thyroid surface, with minimal exposure

Because of the application of "meticulous capsular dissection," how to preserve the parathyroid gland in thyroidectomy has become a minor problem. Because IPTGs enjoy a more variable position in the adult neck and locate in the area of central neck lymph node dissection,

Some methods are recommended to identify and preserve the IPTG [13, 14]. For example, IPTG is superficial to RLN coronal plane and does not dissect the triangular region in order to protect laterally based blood supply of the IPTG (**Figure 6**). However, actually it is not easy to practice.

**Figure 5.** "Meticulous capsular dissection." The distal branches of the inferior thyroid artery medial to the parathyroid at the level of the thyroid capsule, are identified and controlled. Attie's drawing (left); intraoperative view (right); white

of the recurrent laryngeal nerve and disturbance of its blood supply (**Figure 5**).

**3.2. "A layer of thymus, blood vessels and inferior parathyroid gland" in CND**

have to be distinguished from lymph nodes, fatty tissue, and so on.

**3. Two operation concepts during TT and CND**

**3.1. "Meticulous capsular dissection" in thyroid lobectomy**

how to preserve IPTG during CND is a major problem.

arrow: Inferior parathyroid gland; green star: thyroid.

**Figure 3.** Classification of inferior parathyroid gland (by JQ Zhu). Type A (close contact) includes A1 (planar attachment), A2 (embedded attachment) and A3 (intra-thyroid); type B (non-close contact) includes B1 (around thyroid), B2 (intrathymus) and B3 (blood supply from thymus or mediastinum).

**Figure 4.** Intraoperative views of inferior parathyroid gland according Zhu's classification. Type A1 (left upper), A2 (right upper), A3 (left down) and B2 (right down) are included. White arrow: Inferior parathyroid gland; green star: thyroid; blue star: thymus.

(in the second instance of dissection). Therefore, the inferior parathyroid gland can be actually classified into exposure type and unexposure type according to whether the IPTG is identified and preserved during the thyroidectomy (at the first instance). As to the unexposure type, the in situ preservation of the IPTG in CND could be very difficult. This can be attributed to the fact that IPTGs assume a more variable position in the adult neck, thus making their detection difficult. Moreover, IPTGs are located in the area of central neck lymph node dissection and have to be distinguished from lymph nodes, fatty tissue, and so on.
