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Indocyanine green fluorescence angiography for quantitative evaluation of in situ parathyroid gland perfusion and function after total thyroidectomy
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Indocyanine green fluorescence angiography for quantitative evaluation of in situ parathyroid gland perfusion and function after total thyroidectomy Brian Hung-Hin Lang, MS, FRACS,a Carlos K. H. Wong, PhD,b Hing Tsun Hung, MBBS, MRCS,a Kai Pun Wong, MBBS, FRCS,a Ka Lun Mak, MBBS, MRCS,a and Kin Bun Au, MBBS, FRCS,a Hong Kong SAR, China
Background. Because the fluorescent light intensity on an indocyanine green fluorescence angiography reflects the blood perfusion within a focused area, the fluorescent light intensity in the remaining in situ parathyroid glands may predict postoperative hypocalcemia risk after total thyroidectomy. Methods. Seventy patients underwent intraoperative indocyanine green fluorescence angiography after total thyroidectomy. Any parathyroid glands with a vascular pedicle was left in situ while any parathyroid glands without pedicle or inadvertently removed was autotransplanted. After total thyroidectomy, an intravenous 2.5 mg indocyanine green fluorescence angiography was given and realtime fluorescent images of the thyroid bed were recorded using the SPY imaging system (Novadaq, Ontario, Canada). The fluorescent light intensity of each indocyanine green fluorescence angiography as well as the average and greatest fluorescent light intensity in each patient were calculated. Postoperative hypocalcemia was defined as adjusted calcium <2.00 mmol/L within 24 hours. Results. The fluorescent light intensity between discolored and normal-looking indocyanine green fluorescence angiographies was similar (P = .479). No patients with a greatest fluorescent light intensity >150% developed postoperative hypocalcemia while 9 (81.8%) patients with a greatest fluorescent light intensity #150% did. Similarly, no patients with an average fluorescent light intensity >109% developed PH while 9 (30%) with an average fluorescent light intensity #109% did. The greatest fluorescent light intensity was more predictive than day-0 postoperative hypocalcemia (P = .027) and % PTH drop day-0 to 1 (P < .001). Conclusion. Indocyanine green fluorescence angiography is a promising operative adjunct in determining residual parathyroid glands function and predicting postoperative hypocalcemia risk after total thyroidectomy. (Surgery 2016;j:j-j.) From the Division of Endocrine Surgery, Department of Surgery,a Li Ka Shing Faculty of Medicine, The University of Hong Kong; and Department of Family Medicine and Primary Care,b University of Hong Kong, 3/F Ap Lei Chau Clinic, Ap Lei Chau, Hong Kong SAR, China
POSTOPERATIVE HYPOPARATHYROIDISM leading to hypocalcemia (PH) is one of the most common complications after a total thyroidectomy (TT). The Presented as an oral presentation at American Association of Endocrine Surgeons meeting, Baltimore, MD, April 10– 12, 2016. Accepted for publication March 28, 2016. Reprint requests: Brian Hung-Hin Lang, MS, FRACS, Division of Endocrine Surgery, Department of Surgery, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong SAR, China. E-mail: [email protected]. 0039-6060/$ - see front matter Ó 2016 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.surg.2016.03.037
reported incidence ranges from 0–65%, depending on the definition of PH.1-4 Although the cause of PH is multifactorial, one of the most important causes is inadequate or compromised blood supply in the remaining in situ parathyroid glands (ISPGs) from operative manipulation and trauma.1-4 There is, however, no objective intraoperative tool to determine if an ISPG is wellperfused or not. Laser Doppler flowmetry was previously used for assessing parathyroid perfusion, but has not been widely practiced.5 Therefore, surgeons often have to rely on either visual inspection alone (ie, by looking at the color changes in the ISPGs) or the “knife” test as ways SURGERY 1
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of estimating parathyroid perfusion and viability.6,7 Indocyanine green (ICG) is an inert, water soluble, nonradioactive, and nontoxic contrast agent that has been approved by the US Food and Drug Administration since 1959. After intravenous injection, ICG is distributed throughout the intravascular space and rapidly bound to plasma proteins. When illuminated at 806 nm with a low-energy laser, these plasma-bound ICG molecules become fluorescent and this fluorescence is recorded by a charge-coupled device camera. Because the fluorescence intensity (FI) in a focused area is directly proportional to the perfusion in that area, the FI value of the ISPGs measured on the ICG fluorescence angiography (ICGA) may provide information regarding to the perfusion and the extent of viability of the ISPGs.8-10 This technology is actually not new and has been used in various clinical areas,8-10 including assessing perfusion of skin flaps, bowel anastomosis, and lower limbs. Although this technique has been used for assessing parathyroid remnant in subtotal parathyroidectomy,11 to our knowledge, its use in assessing parathyroid perfusion during thyroid operation has never been reported. We hypothesized that the fluorescent intensity (FI) in the ISPGs may reflect not only the perfusion of the ISPGs, but also the residual parathyroid function and the subsequent risk of PH. Given that parathyroid perfusion plays a vital role in normalizing early parathyroid function, perhaps patients with a greater FI value in their ISPGs (ie, good parathyroid perfusion) have a lower chance of PH than those with a lower FI value. Our study aimed to examine the relationship between the greatest and overall average FI taken from the remaining ISPGs and the risk of PH after TT. METHODS AND PATIENTS Ninety-four consecutive patients agreed and underwent intraoperative ICGA after a primary TT. For the present study, one surgeon performed all the procedures and during the operation, the surgeon attempted to identify and leave as many vascularized parathyroid glands (PGs) as possible by carefully preserving their attached vascular pedicle. Those PGs that could not have their blood pedicle preserved or were inadvertently removed during operation were autotransplanted. Before the ICGA, to confirm that each identified PG (in situ or transplanted) was really a PG and not mistaken as a thyroid nodule, lymph node, or fat, a small puff of tissue was taken, fixed, and sent for
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Fig 1. A colorized mode image of the left superior in situ parathyroid gland (91%) and the anterior trachea (100%).
paraffin section. After the biopsy, the tissue was marked with a metal clip. For analysis, only patients with 4 biopsy-confirmed PGs were eligible for analysis. Patients with $1 biopsies containing non-PG tissue were excluded. Operative technique. Operative techniques and postoperative care were standardized throughout.7,12 All thyroidectomies were performed under general anesthesia. To preserve the blood supply of each PG, careful extracapsular dissection was performed. Each terminal branch of the thyroid artery or vein was ligated individually close to capsule distal to the PG using 4-0 ties. No energy devices (including electrocautery) were used when dissecting close to the PGs. After the entire thyroid gland had been removed, the specimen was inspected for any missing PGs. Any PGs that had been inadvertently devascularized or removed were immediately taken out, minced, and autotransplanted into the ipsilateral sternocleidomastoid muscle. Appearance of each PG (normal/discolored) was noted before closure of wound.7 During the study period, the same group of pathologists examined all excised thyroid specimens for inadvertently removed PG. Intraoperative ICGA. After the entire thyroid gland had been removed, an intraoperative ICGA was performed using the SPY Fluorescent Imaging system (Novadaq Technologies, Inc, Mississauga, Ontario, Canada). This system consists of an imaging head equipped with a charge-coupled device camera, a laser light source, and a distance sensor. The laser operates at a power density of 40 mW/cm2 and because the camera head has a proximity limitation of 5 cm from the area of interest (ie, the thyroid bed) to prevent
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Fig 2. A picture showing similar indocyanine green perfusion pattern between an in situ parathyroid gland (ISPG) and anterior trachea of the same patient.
overexposure, during each ICGA, the camera head was positioned approximately 15–20 cm away from the thyroid bed. Once the imaging head was positioned correctly, a fixed-dose of ICG (2.5 mg) was given intravenously by the anesthetist. Real-time fluorescent images of the entire thyroid bed were then recorded approximately 15 seconds after the injection. Images were recorded by the charge-coupled device camera and were viewed in the heat-map (or colorized) mode where red indicates high intensity and blue indicates low intensity. To confirm what was seen on the real-time images was an ISPG and not a blood vessel or remnant thyroid tissue, the surgeon manually picked up each identifiable ISPG during the recording. Because each identifiable ISPG was clipped after the biopsy, the attached metal clip helped with the identification of the ISPG on the images. After all identifiable ISPGs had been clearly seen, the recording was stopped. To calculate the FI of each identifiable ISPG, the recorded images were played back in the operating theater (while the patient was still under anesthesia) and 2 image cursors were used to measure the intensity of the ISPG and the anterior trachea. The FI of each identifiable ISPG was expressed as an intensity ratio between it and the anterior trachea (which was taken as 100%; Fig 1). These calculations were finalized while the patient was still under anesthesia. The reasons for choosing the anterior trachea as the reference point were: 1) the anterior trachea was the most constant and exposed part of the thyroid bed, and 2) both the ISPG and the anterior trachea share similar perfusion characteristics (ie, ingress and egress rates; Fig 2) and the ratio between the 2 remained relatively constant throughout the postinjection period. The greatest FI value of a patient (greatest FI) was defined as the greatest FI value recorded among the
remaining ISPGs while the overall average FI of a patient (average FI) was the sum of FI of all PGs divided by 4. Any PGs that were taken out and autotransplanted were given a FI value of zero because no immediate perfusion was expected. Postoperative management and follow-up. Serum PTH, calcium (Ca) and phosphate (PO4) levels were checked preoperatively, immediately after operation (day-0), and on the following morning (day-1). PH was defined as serum adjusted Ca <2.00 mmol/L within 24 hours of TT (range, 2.11–2.55 mmol/L). Oral Ca ± calcitriol were not routinely given unless adjusted Ca <2.00 mmol/L or patients had symptoms. Under these circumstances, Oscal 1,500–3,000 mg ± calcitriol 0.25 mcg twice daily were prescribed until first clinic visit 1– 2 weeks later. Patients requiring Ca ± calcitriol supplements after their first postoperative visit were followed-up and had their calcium and PTH checked every 4 weeks until they could maintain normocalcemia without supplements (ie, completely weaned off their supplements).12 Laboratory methods. Serum albumin-adjusted Ca and phosphate levels were measured in the hospital laboratory by standard methods using the Roche Diagnostics Modular Analytic system (Roche Diagnostics, Indianapolis, IN). PTH level was measured by Access 2 immunoassay system (Beckman Coulter, Brea, CA), and the inter- and intra-assay CVs were 5.8 and 4.5%, respectively. The normal range for serum PTH level was 1.2–5.7 pmol/L (to convert pmol/L to pg/mL, divide by 0.106). Serum 25-hydroxyvitamin D was measured by using the electrochemiluminescence immunoassay (Elecsys Vitamin D Total assay), and the interand intra-assay CVs were 6.2 and 4.8%, respectively. The measuring range was 3.00–70.0 ng/mL (to convert ng/mL to nmol/L, multiply by 2.496).
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Statistical analysis. For comparison of categorical variables, v2 tests, and Fisher exact tests were used while for comparison of continuous variables, the Mann-Whitney U was used. For correlation between 2 continuous variables, the Pearson correlation test was performed. To improve clinical utility of continuous variables, Youden index was used to calculate the best cut-off value for predicting hypocalcemia. The area under the receiver-operating curve (AUC) was used to measure the predictability. AUC values closer to 1 meant better predictability, whereas values closer to 0.5 meant poorer predictability. The AUCs were compared using the Delong test.13 All statistical analyses were performed using SPSS version 18.0 (SPSS, Chicago, IL) and the STATA software version 13 (STATA, College Station, TX). P < .05 was considered statistically significant. RESULTS Altogether 94 consecutive patients underwent a successful ICGA after a primary TT. Among these 94 patients, 340 PGs were identified and 324 (95.3%) PGs were later confirmed to be PG on histology. Therefore, only 70 (74.5%) patients had 4 identifiable PGs confirmed on histology and were eligible for analysis. None of these patients had parathyroid tissue or gland inadvertently found on the excised thyroid specimen. Five (7.1%) patients underwent PG autotransplantation. Four patients had 1 PG transplanted and another had 2 PGs transplanted. Table I shows the baseline characteristics and perioperative biochemical changes of these 70 patients. Nine (12.9%) patients developed PH, and all except one patient were able to be weaned off Ca ± calcitriol supplements within 4 weeks of operation. That patient was eventually weaned off Ca ± calcitriol supplements 3 months after operation. No patient had permanent PH (ie, >6 months). In terms of the FI of each identified PG relative to its location and glandular appearance, the mean FI of the left lower PGs was significantly less than that of the right upper PGs (97.36 ± 83.46% vs 135.79 ± 88.64%, P = .007) and left upper PGs (97.36 ± 83.46% vs 134.45 ± 101.95%, P = .028). Also, the upper PGs had significantly greater FIs than the lesser PGs (135.12 ± 95.18% vs 113.15 ± 97.06%, P = .025). In terms of glandular appearance and its correlation with FI, among the 274 ISPGs, 143 (52.2%) seemed discolored at the end of operation while the rest (n = 131) remained normal-looking. The FI value between the discolored and normal-looking ISPGs was similar
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Table I. Baseline characteristics and biochemical changes after total thyroidectomy Parameters Age at operation (y) Sex (male:female) Operative indication Benign pathology Graves’ disease/toxic goiter Indeterminate cytology Malignancy Weight of excised gland (g) Total operating time (min) Total time taken for the ICGA (min) Estimated blood loss (mL) No. of patients with 2 ISPGs 3 ISPGs 4 ISPGs No. of patients with No PG auto-transplanted 1 PG auto-transplanted 2 PGs auto-transplanted Preoperative adjusted calcium (mmol/L) Preoperative 25-hydroxyvitamin D3 (ng/mL)* Postoperative day-0 adjusted serum calcium (mmol/L) Postoperative day-1 adjusted serum calcium (mmol/L) No. of patients with postoperative hypocalcemia (adjusted serum calcium #2.00 mmol/L) Adjusted Ca drop from preoperative to postoperative day-0 (%) Adjusted Ca drop from preoperative to postoperative day-1 (%) Preoperative PTH (Pre-PTH) (pmol/L)y Postoperative PTH on postoperative day-0 (PTH-D0) (pmol/L)y Postoperative PTH on postoperative day-1 (PTH-D1) (pmol/L)y
Total no. of patients (n = 70) 54.5 ± 15.0 13:57 38 (54.3) 15 (21.4) 5 (7.1) 12 (17.1) 50.4 ± 48.9 109.1 ± 49.8 2.7 ± 0.5 17.6 ± 14.9 1 (1.4) 4 (5.7) 65 (92.9) 65 (92.9) 4 (5.7) 1 (1.4) 2.32 ± 0.80 47.55 ± 185.40 2.21 ± 0.80 2.16 ± 0.13 9 (15.7)
4.54 ± 3.55 6.12 ± 5.63 9.41 ± 4.78 4.60 ± 3.03 2.50 ± 1.97
*For vitamin D3, multiply ng/mL by 2.496 get nmol/L. yFor PTH, divide pmol/L by 0.106 to get pg/mL. ICGA, Indocyanine green fluorescence angiography; ISPG, in situ parathyroid gland; Ca, calcium; PTH, parathyroid hormone.
(133.45 ± 98.0% vs 121.44 ± 94.16%, P = .479). The FI for normal-looking ISPGs ranged from 12–335 while the ICG for discolored ISPGs ranged from 0–307. There was no normal-looking ISPG with zero uptake while there was one discolored ISPG with zero uptake. In terms of patients, the median (range) greatest FI of each patient was 208.50% (105.00–419.00) while the median
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Fig 3. A diagram showing the relationship between the greatest and average fluorescence intensity and risk of postoperative hypocalcemia; 150% and 85% were optimal cut-off values for greatest and average fluorescence intensity, respectively.
(range) average FI of each patient was 155.80% (55.50–320.00). There were significant correlations between greatest FI and PTH-D0 (r = 0.081, P < .001), greatest FI and PTH-D1 (r = 0.598, P < .001) and greatest FI and % drop in PTH from preoperative to day-0 (r = 0.239, P < .001), but interestingly, not between average FI and PTH-D0 (r = 0.109, P = .371), average PTH-D1 (r = 0.106, P = .384) and average FI and % drop in PTH from preoperative to day-0 (r = 0.115, P = .345). Figure 3 shows the relationship between FI values and PH. When a patient had the greatest FI value >150%, the chance of PH was zero (0/ 59), and when the greatest FI value was # 150%, 9 (81.8%) developed PH. The 2 patients with the greatest FI value #150% that did not develop PH (ie, normocalcemia) had a greatest FI value of 116% and 119%, respectively. Their average FI value were 56.25% and 112.0%, respectively. Similarly, when a patient had the average FI value >109%, the chance of PH was zero (0/40), but when the overall average FI was <109%, 9/30 (30.0%) developed PH. Table II shows the 9 patients who developed temporary PH after TT. Table III compares the test sensitivity, specificity, and predictability (AUC) between various tests using their optimal cut-off value. The greatest FI value (#150% and >150%) had the greatest sensitivity, specificity, and predictability relative to the other tests. As a predictive test, the greatest FI was superior to PTH-D0 (P = .027) and % PTH drop from day0 to 1 (P < .001). Also, although not significant, the greatest FI tended to be superior to the average FI (P = .073).
Table IV shows the results of using a combined greatest and average FI to predict PH. There was no significance difference in the rate of PH between average FI >85% and average # 85% when the greatest FI was # 150% (80.0% vs 83.3%, P = 1.000). DISCUSSION ICG is a safe and inexpensive dye that has been used for a variety of medical conditions.8-10 In thyroid operation, it has been described as a useful contrast agent for PG identification.14 Although one group11 has recently reported using the PINPOINT camera (Novadaq, Mississauga, ON, Canada) to assess perfusion, it does not provide the surgeon a numeric value of the perfusion, and our system does. To our knowledge, this is the first report to use ICG as a potential perfusion marker during thyroid operation. It works based on the principle that an intravascular ICG molecule becomes fluorescent when exposed to light at wavelengths between 750–800 nm and the intensity of this emitted fluorescence (ie, FI) measured by a charge-coupled camera directly reflects the amount of perfusion within that focused area.8-10 As a result, we hypothesized that patients with a greatest FI value in their ISPGs would have greater parathyroid perfusion and residual function and therefore, lesser risk of PH than those with a lesser FI value. Our data confirmed this hypothesis by first showing that there were significant correlations between the greatest FI and PTH-D0 (r = .081, P < .001), greatest FI and PTH-D1 (r = .598, P < .001) and greatest FI and % drop in PTH from preoperative to day-0 (r = 0.239,
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80.00 66.80 94.71 94.07 96.67 91.55 98.10 95.00 82.31 11.00 3.00 3.00 3.00 3.00 3.00 14.00 15.00 8.00 28.51 28.86 9.00 27.00 5.00 6.00 19.00 43.00 17.00 2.00 1.95 1.76 1.92 1.98 1.90 2.00 2.00 1.96 2.24 2.23 2.03 2.12 2.15 2.09 2.28 2.21 2.38 85.25 84.25 61.25 74.75 99.00 108.5 63.50 97.25 50.75 149 148 111 133 146 140 105 129 110 149 69 89 34 101 88 148 0* 111 14 97 23 133 49 86 31 133 146 55 62 124 140 91 79 105 51 75 23 41 107 112 129 42 40 11 110 0 1 0 0 0 0 0 0 0 Indeterminate Benign Graves’ Graves’ Benign Benign Benign Benign Benign
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*Autotransplanted. PG, Parathyroid gland; FI, fluorescence intensity measured on indocyanine green angiography; RU, right upper parathyroid; RL, right lower parathyroid; LU, left upper parathyroid; LL, left lower parathyroid; Ca-D0, calcium on day-0; Ca-D1, calcium on following morning; PTH-D0, PTH taken immediately after operation; PTH-D1, PTH taken on the following morning; preop, preoperative; D0, postoperative day-0.
Age (y)/sex
67/F 37/F 61/F 48/F 58/F 36/F 55/F 45/F 50/F
Greatest Mean Adjusted Ca-D0 Adjusted PTH-D0 PTH-D1 PTH drop from FI value (%) FI value (%) (mmol/L) Ca-D1 (mmol/L) (pmol/L) (pmol/L) preop to D0 (%) LL LU RL RU
FI of PG (%)
No. of PGs transplanted Operative indication
Table II. Summary of the 9 patients who developed postoperative hypocalcemia (ie, serum adjusted calcium # 2.00 mmol/L)
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P < .001). Second, when the greatest FI was > 150% (ie, a FI >150% in at least 1 ISPGs), the risk of developing subsequent PH was 0/59 (0.0%) while when the greatest FI was #150% (ie, none of the ISPGs exhibited a FI >150%), the chance of PH was 9/11 (81.8%). Similarly, when the average FI was >109%, the chance of PH was also 0/40 (0.0%). However, it is worth noting that the average FI was less predictive of PH than the greatest FI (AUC 0.81 vs AUC 0.98, P = .073; Table III). Indeed, our data showed that only 30% of patients developed PH when the average FI was <109% while >80% developed PH when the greatest FI was #150%. Even when an optimal cut-off of 85% was used, only 5/10 (50.0%) developed PH when the average FI was # 85%. Interestingly, among those with greatest FI # 150%, the difference in PH risk was not statistically different between those having average FI >85% and those having average FI # 85% (80.0% vs 83.3%, P = 1.00; Table IV). In other words, measuring the average FI did not significantly add to the overall predictability relative to using greatest FI alone. The implication is that perhaps in the future, finding one wellperfused PG (with a FI >150%) at operation might be sufficient in ruling out the subsequent risk of PH. However, given that this is the first report using FI to predict PH, additional studies are required to confirm this finding. Furthermore, the reason why using greatest FI might be more predictive of PH than average FI remains unexplained. We postulate that perhaps having one well-perfused PG (ie, FI >150%) intraoperatively may offer more resistance to the development of PH than having several less-perfused PGs (FI <150%) after TT. Perhaps future studies could focus on how individual PG functions biochemically when the measured FI of a PG is >150% and #150%. Another finding worth highlighting was that the overall predictability (by AUC) in the greatest FI was superior to PTH-D0 (P = .027) and % PTH drop from D0 to D1 (P < .001). This is important given that these latter tests have been used to guide PH management and facilitate early hospital discharge.15,16 Therefore, measuring the FI on ICGA could be an alternative method in predicting PH and facilitating early hospital discharge after TT. Furthermore, given its potential in distinguishing between well-perfused and less well-perfused PGs, it allows the surgeon to decide which of the ISPGs should be autotransplanted or left in situ. Given that visual inspection is subjective and unreliable,6,7 this could become a new tool for selecting
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Table III. Comparison of different tests in predicting postoperative hypocalcemia (PH) Optimal cut-off value* Greatest FI value on ICGA (%) Average FI value on ICGA (%) PTH on day-0 (pmol/L) PTH on day-1 (pmol/L) PTH drop from preoperative to day-0 (%) PTH drop from day-0 to day-1 (%)
#150 #85 #1.5 #3.0 $80.0 $40.0
Sensitivity (%) 9/9 5/9 6/9 9/9 7/9 6/9
(100) (55.6) (66.7) (100) (77.8) (66.7)
Specificity (%)
AUCy
95% CI
59/61 56/61 56/61 23/61 57/61 33/61
0.98 0.81 0.85 0.87 0.96 0.58
0.95–1.00 0.62–0.99 0.73–0.96 0.76–0.99 0.90–1.00 0.38–0.79
(96.7) (91.8) (91.8) (37.7) (93.4) (54.1)
*Determined by the receiver operating characteristic curve and Youden index. yValues closer to 1.00 indicate better predictability, whereas closer to 0.50 indicate poorer predictability. By DeLong test, the greatest FI was more predictive of PH than in the greatest FI was superior to PTH-D0 (P = .027) and % PTH drop from day-0 to 1 (P < .001). ICGA, Indocyanine green angiography; AUC, area under the receiver-operating curve; FI, fluorescence intensity; PTH, parathyroid hormone.
Table IV. Using a combination of greatest FI and average FI measured during ICGA to predict PH
Outcome
Greatest FI > 150 and average FI >85
Greatest FI > 150 and average FI # 85
Greatest FI # 150 and average FI >85
Greatest FI # 150 and average FI #85
Total
No PH* (%) PH* (%) Total
55 (100.0) 0 (0.0) 55
4 (100.0) 0 (0.0) 4
1 (20.0) 4 (80.0) 5
1 (16.7) 5 (83.3) 6
61 (87.1) 9 (12.9) 70
*PH defined as serum adjusted Ca <2.00 mol/L at 24-hour after total thyroidectomy and/or need for oral Ca ± calcitriol supplements to maintain normocalcemia. FI, Fluorescence intensity; PTH, parathyroid hormone.
patients for parathyroid autotransplantation. For example, those PGs with very low FI value could be taken out and autotransplanted while those with FI >150 might be better left in situ (regardless of its appearance). Another potential application would be to perform ICGA immediately after completing the first side of a TT. This would give the surgeon a better idea on the residual parathyroid function in the first completed side before proceeding to the second side of the TT. This approach may prove to be effective in avoiding longer-term PH in the future. However, at this time, more work needs to be done to define an ISPG as being well-perfused or poorly perfused based on the FI value alone. Our data did not find a significant correlation between the naked eye assessment (ie, color change) and ICG assessment (P = .479). One of the interesting findings was the observed differences in FI among the ISPGs. This may have implications in subtotal parathyroidectomy where perhaps, the one with the greatest FI might be the preferred remnant over the other ISPGs with lower FI.11 In terms of costs, after including the maintenance cost of the SPY imaging system and consumables (including nonreusable plastic drape and
ICG dye) used during the procedure, one ICGA cost around US $253. This is roughly twice the cost of a PTH test (US $120) at our institution. However, given its potential in better selecting patients for parathyroid auto-transplantation and possibly reducing longer-term PH, it may be a costeffectiveness tool. It is worth highlighting that the ICGA is not a perfect predictive tool as there were 2 (2.9%) patients with low FIs who did not develop PH. One patient, in fact, had an average FI of 56.25% and a greatest FI of 119%. For these 2 patients, measurement errors were possible. Furthermore, despite these findings, there were several shortcomings with the present study. First, because this was a single institution study conducted by one surgeon, its applicability in other centers remains unconfirmed. Second, due to the small number of patients and events (such as permanent PH), our study was prone to type II error and it remains unknown how ICGA may affect rate of PH in the longer-term. Third, it should be noted that biopsying all 4 PGs during TT was simply done for the purpose of the study and given the high rate of concordance between visual identification and histology (95.3%), in the future we would proceed to the ICGA without biopsy. However, given that
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biopsy was done in the present study, the FI value might be different from that without the biopsy. Discolored and normal-looking ISPGs had similar FI values on ICGA (133.45 ± 98.0% vs 121.44 ± 94.16%, P = .479). Given that no patients with the greatest FI >150% or average FI >109% developed PH, the ICGA may be a promising operative adjunct in determining residual parathyroid function and predicting the risk of PH. In terms of future applications, this new tool may have a role in selecting patients for parathyroid autotransplantation and guiding surgeons in their approach to the second side of a TT. We would like to thank Dr Tony Shek and his team of pathologists for carefully examining all the excised thyroid specimens during this study period.
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16.
or vitamin D supplementation after total thyroidectomy? World J Surg 2013;37:2581-8. DeLong ER, DeLong DM, Clarke–Pearson DL. Comparing the areas under two or more correlated receiver operating characteristic curves: a nonparametric approach. Biometrics 1988;44:837-45. Suh YJ, Choi JY, Chai YJ, Kwon H, Woo JW, Kim SJ, et al. Indocyanine green as a near-infrared fluorescent agent for identifying parathyroid glands during thyroid surgery in dogs. Surg Endosc 2015;29:2811-7. Grodski S, Serpell J. Evidence for the role of perioperative PTH measurement after total thyroidectomy as a predictor of hypocalcemia. World J Surg 2008;32:1367-73. Lang BH, Yih PC, Ng KK. A prospective evaluation of quick intraoperative parathyroid hormone assay at the time of skin closure in predicting clinically relevant hypocalcemia after thyroidectomy. World J Surg 2012;36:1300-6.
DISCUSSION Dr Richard A. Prinz (Evanston, IL): Brian, a very, very nice study. I have a number of questions. Now, you biopsied all of your glands and you only used this technique according to your protocol when four glands were identified. So do you think biopsy is necessary? And what do you do if you have not identified all four glands? Is it still a useful technique? And then it seems like you are using this for a method to determine if you need to autotransplant a gland. Did your rate or the number of parathyroid autotransplantations increase with this technique compared to what your historical rates were? Thank you. Dr Brian H. Lang: For your first question related to the biopsy, this was done basically for the study because we want to make sure that what we are seeing was a parathyroid gland and it was not something else like a lymph node or a thyroid nodule. For your second question, the rate of autotransplantation actually has been the same as before. It is around 5% for our own series, before and after the study. So we have not increased the autotransplant rate, and that is because the principle of autotransplantation has not really changed. Basically, if we see a gland that has a vascular pedicle, we would leave it in situ. We will not autotransplant it. Dr Samuel K. Snyder (Temple, TX): Thank you for a very interesting study. You have given us a new concept for evaluating adequate vascularity of the parathyroid intraoperatively. I just have 2 quick questions. One is, a common problem is hematoma on the parathyroid. And my question is, does the development of a hematoma or a bruising on the surface of the parathyroid, not necessarily ischemia but bruising, affect your fluorescence levels?
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Secondly, did you introduce a control mechanism? Because most of us when we do parathyroid surgery, we look at the parathyroids and we say, you know, they look good. I do not think this patient is going to have a problem postop. You had the option of doing that before you did your fluorescence and then compare the surgeon’s perception as to what the vascularity was going to be and then whether or not the technique actually introduced extra information that helped you. Dr Brian H. Lang: Essentially when we compared---first of all, visual inspection could be very subjective. Something that is discolored for you may be different for another surgeon. Essentially, all the procedures were done by me. Essentially, I compared the fluorescence intensity of a discolored gland, which could or could not have a hematoma, and also a normal-looking gland. Essentially we found there was no statistical significance in the fluorescence intensity between the normal-looking and the bruised gland. So it probably supports your concept that probably these bruised glands are actually just bruised and they are not ischemic. Dr Janice L. Pasieka (Calgary, AB): Brian, wonderful presentation. Could you comment on how you got this through ethics? If we go back to the days of a 4 gland exploration, we know that by biopsying all of our normal glands, or the remaining 3 normal glands, increased the rate of hypocalcemia postoperatively. So how did you get that through ethics? My second question is, you are an experienced endocrine surgeon. You know what a parathyroid looks like most of the time. Have you now moved to not biopsying it and using this technique in your practice day to day? Dr Brian H. Lang: Basically, it was not a large biopsy. It was a shaving of the capsule of the gland. So we do not think that that actually induces iatrogenic hypocalcemia. Also, the reason for doing biopsy was because sometimes it is very difficult to know whether it is a real para or not. If you look at our data more closely, there is a 93% concordance. So we are correct probably 9 out of 10 times. But having said that, there was still a 10% difference, and that is the reason for doing the biopsy. We do not routinely biopsy a parathyroid gland, but for this study, we did.
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Dr Quan-Yang Duh (San Francisco, CA): Brian, wonderful study. And conceptually I looked at this test very similar to neuromonitoring. And when we do neuromonitoring, you know, people argue about whether or not we need it or do not need it. This is the other complication that we all dread for patients with thyroidectomy. The difference is in neuromonitoring you can do it, do your operation, repeat it, do your operation, et cetera, or you can do continuous monitoring. The question I have for you is, how often can you do the injection? So I inject it once. I looked at the thing. How many minutes do I have to wait? Can I do another one? Dr Brian H. Lang: It has a half-life, so you can repeat every 30 minutes. So you can do it before you remove the thyroid gland and do it after the operation. You can do it a couple of times. It does not matter. It gets washed out pretty quickly. Dr Quan-Yang Duh (San Francisco, CA): So give me an example of a case that you do. How many times do you inject indocyanine green? Dr Brian H. Lang: For this study, we only inject once. It was immediately after the total thyroidectomy. But potentially this could be done several times. So you can complete one side of the total thyroidectomy and you can do the ICG on that side and see the 2 parathyroid glands before you proceed to the opposite side. So this is an advantage. Dr Quan-Yang Duh (San Francisco, CA): So there is no issue of toxicity? Dr Brian H. Lang: No. Dr James G. Norman (Tampa, FL): I think it is important to note against the conversation that is happening here, it is really important to differentiate between thyroid surgery and parathyroid surgery. I agree with Dr Pasieka, what she says about biopsying parathyroid glands during thyroid surgery. I do not see much role in that. But we have to clarify this age-old adage that biopsying of parathyroid glands, like during parathyroid surgery, has an increased effect on hypoparathyroidism, hypocalcemia. It is nonsense. We cannot continue that type of nonsense. We biopsy all 4 parathyroid glands in every patient and have done so for decades. Absolutely does not cause hypoparathyroidism.
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Indocyanine green fluorescence angiography for quantitative evaluation of in situ parathyroid gland perfusion and function after total thyroidectomy Brian Hung-Hin Lang, MS, FRACS, Carlos K. H. Wong, PhD, Hing Tsun Hung, MBBS, MRCS, Kai Pun Wong, MBBS, FRCS, Ka Lun Mak, MBBS, MRCS, and Kin Bun Au, MBBS, FRCS, Hong Kong SAR, China A total of 70 patients underwent intraoperative indocyanine green angiography after total thyroidectomy. Our data showed that indocyanine green angiography is a promising operative adjunct for predicting biochemical hypocalcemia after total thyroidectomy.
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Indocyanine green fluorescence angiography for quantitative evaluation of in situ parathyroid gland perfusion and function after total thyroidectomy Brian Hung-Hin Lang, MS, FRACS,a Carlos K. H. Wong, PhD,b Hing Tsun Hung, MBBS, MRCS,a Kai Pun Wong, MBBS, FRCS,a Ka Lun Mak, MBBS, MRCS,a and Kin Bun Au, MBBS, FRCS,a Hong Kong SAR, China
Background. Because the fluorescent light intensity on an indocyanine green fluorescence angiography reflects the blood perfusion within a focused area, the fluorescent light intensity in the remaining in situ parathyroid glands may predict postoperative hypocalcemia risk after total thyroidectomy. Methods. Seventy patients underwent intraoperative indocyanine green fluorescence angiography after total thyroidectomy. Any parathyroid glands with a vascular pedicle was left in situ while any parathyroid glands without pedicle or inadvertently removed was autotransplanted. After total thyroidectomy, an intravenous 2.5 mg indocyanine green fluorescence angiography was given and realtime fluorescent images of the thyroid bed were recorded using the SPY imaging system (Novadaq, Ontario, Canada). The fluorescent light intensity of each indocyanine green fluorescence angiography as well as the average and greatest fluorescent light intensity in each patient were calculated. Postoperative hypocalcemia was defined as adjusted calcium <2.00 mmol/L within 24 hours. Results. The fluorescent light intensity between discolored and normal-looking indocyanine green fluorescence angiographies was similar (P = .479). No patients with a greatest fluorescent light intensity >150% developed postoperative hypocalcemia while 9 (81.8%) patients with a greatest fluorescent light intensity #150% did. Similarly, no patients with an average fluorescent light intensity >109% developed PH while 9 (30%) with an average fluorescent light intensity #109% did. The greatest fluorescent light intensity was more predictive than day-0 postoperative hypocalcemia (P = .027) and % PTH drop day-0 to 1 (P < .001). Conclusion. Indocyanine green fluorescence angiography is a promising operative adjunct in determining residual parathyroid glands function and predicting postoperative hypocalcemia risk after total thyroidectomy. (Surgery 2016;j:j-j.) From the Division of Endocrine Surgery, Department of Surgery,a Li Ka Shing Faculty of Medicine, The University of Hong Kong; and Department of Family Medicine and Primary Care,b University of Hong Kong, 3/F Ap Lei Chau Clinic, Ap Lei Chau, Hong Kong SAR, China
POSTOPERATIVE HYPOPARATHYROIDISM leading to hypocalcemia (PH) is one of the most common complications after a total thyroidectomy (TT). The Presented as an oral presentation at American Association of Endocrine Surgeons meeting, Baltimore, MD, April 10– 12, 2016. Accepted for publication March 28, 2016. Reprint requests: Brian Hung-Hin Lang, MS, FRACS, Division of Endocrine Surgery, Department of Surgery, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong SAR, China. E-mail: [email protected]. 0039-6060/$ - see front matter Ó 2016 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.surg.2016.03.037
reported incidence ranges from 0–65%, depending on the definition of PH.1-4 Although the cause of PH is multifactorial, one of the most important causes is inadequate or compromised blood supply in the remaining in situ parathyroid glands (ISPGs) from operative manipulation and trauma.1-4 There is, however, no objective intraoperative tool to determine if an ISPG is wellperfused or not. Laser Doppler flowmetry was previously used for assessing parathyroid perfusion, but has not been widely practiced.5 Therefore, surgeons often have to rely on either visual inspection alone (ie, by looking at the color changes in the ISPGs) or the “knife” test as ways SURGERY 1
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of estimating parathyroid perfusion and viability.6,7 Indocyanine green (ICG) is an inert, water soluble, nonradioactive, and nontoxic contrast agent that has been approved by the US Food and Drug Administration since 1959. After intravenous injection, ICG is distributed throughout the intravascular space and rapidly bound to plasma proteins. When illuminated at 806 nm with a low-energy laser, these plasma-bound ICG molecules become fluorescent and this fluorescence is recorded by a charge-coupled device camera. Because the fluorescence intensity (FI) in a focused area is directly proportional to the perfusion in that area, the FI value of the ISPGs measured on the ICG fluorescence angiography (ICGA) may provide information regarding to the perfusion and the extent of viability of the ISPGs.8-10 This technology is actually not new and has been used in various clinical areas,8-10 including assessing perfusion of skin flaps, bowel anastomosis, and lower limbs. Although this technique has been used for assessing parathyroid remnant in subtotal parathyroidectomy,11 to our knowledge, its use in assessing parathyroid perfusion during thyroid operation has never been reported. We hypothesized that the fluorescent intensity (FI) in the ISPGs may reflect not only the perfusion of the ISPGs, but also the residual parathyroid function and the subsequent risk of PH. Given that parathyroid perfusion plays a vital role in normalizing early parathyroid function, perhaps patients with a greater FI value in their ISPGs (ie, good parathyroid perfusion) have a lower chance of PH than those with a lower FI value. Our study aimed to examine the relationship between the greatest and overall average FI taken from the remaining ISPGs and the risk of PH after TT. METHODS AND PATIENTS Ninety-four consecutive patients agreed and underwent intraoperative ICGA after a primary TT. For the present study, one surgeon performed all the procedures and during the operation, the surgeon attempted to identify and leave as many vascularized parathyroid glands (PGs) as possible by carefully preserving their attached vascular pedicle. Those PGs that could not have their blood pedicle preserved or were inadvertently removed during operation were autotransplanted. Before the ICGA, to confirm that each identified PG (in situ or transplanted) was really a PG and not mistaken as a thyroid nodule, lymph node, or fat, a small puff of tissue was taken, fixed, and sent for
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Fig 1. A colorized mode image of the left superior in situ parathyroid gland (91%) and the anterior trachea (100%).
paraffin section. After the biopsy, the tissue was marked with a metal clip. For analysis, only patients with 4 biopsy-confirmed PGs were eligible for analysis. Patients with $1 biopsies containing non-PG tissue were excluded. Operative technique. Operative techniques and postoperative care were standardized throughout.7,12 All thyroidectomies were performed under general anesthesia. To preserve the blood supply of each PG, careful extracapsular dissection was performed. Each terminal branch of the thyroid artery or vein was ligated individually close to capsule distal to the PG using 4-0 ties. No energy devices (including electrocautery) were used when dissecting close to the PGs. After the entire thyroid gland had been removed, the specimen was inspected for any missing PGs. Any PGs that had been inadvertently devascularized or removed were immediately taken out, minced, and autotransplanted into the ipsilateral sternocleidomastoid muscle. Appearance of each PG (normal/discolored) was noted before closure of wound.7 During the study period, the same group of pathologists examined all excised thyroid specimens for inadvertently removed PG. Intraoperative ICGA. After the entire thyroid gland had been removed, an intraoperative ICGA was performed using the SPY Fluorescent Imaging system (Novadaq Technologies, Inc, Mississauga, Ontario, Canada). This system consists of an imaging head equipped with a charge-coupled device camera, a laser light source, and a distance sensor. The laser operates at a power density of 40 mW/cm2 and because the camera head has a proximity limitation of 5 cm from the area of interest (ie, the thyroid bed) to prevent
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Fig 2. A picture showing similar indocyanine green perfusion pattern between an in situ parathyroid gland (ISPG) and anterior trachea of the same patient.
overexposure, during each ICGA, the camera head was positioned approximately 15–20 cm away from the thyroid bed. Once the imaging head was positioned correctly, a fixed-dose of ICG (2.5 mg) was given intravenously by the anesthetist. Real-time fluorescent images of the entire thyroid bed were then recorded approximately 15 seconds after the injection. Images were recorded by the charge-coupled device camera and were viewed in the heat-map (or colorized) mode where red indicates high intensity and blue indicates low intensity. To confirm what was seen on the real-time images was an ISPG and not a blood vessel or remnant thyroid tissue, the surgeon manually picked up each identifiable ISPG during the recording. Because each identifiable ISPG was clipped after the biopsy, the attached metal clip helped with the identification of the ISPG on the images. After all identifiable ISPGs had been clearly seen, the recording was stopped. To calculate the FI of each identifiable ISPG, the recorded images were played back in the operating theater (while the patient was still under anesthesia) and 2 image cursors were used to measure the intensity of the ISPG and the anterior trachea. The FI of each identifiable ISPG was expressed as an intensity ratio between it and the anterior trachea (which was taken as 100%; Fig 1). These calculations were finalized while the patient was still under anesthesia. The reasons for choosing the anterior trachea as the reference point were: 1) the anterior trachea was the most constant and exposed part of the thyroid bed, and 2) both the ISPG and the anterior trachea share similar perfusion characteristics (ie, ingress and egress rates; Fig 2) and the ratio between the 2 remained relatively constant throughout the postinjection period. The greatest FI value of a patient (greatest FI) was defined as the greatest FI value recorded among the
remaining ISPGs while the overall average FI of a patient (average FI) was the sum of FI of all PGs divided by 4. Any PGs that were taken out and autotransplanted were given a FI value of zero because no immediate perfusion was expected. Postoperative management and follow-up. Serum PTH, calcium (Ca) and phosphate (PO4) levels were checked preoperatively, immediately after operation (day-0), and on the following morning (day-1). PH was defined as serum adjusted Ca <2.00 mmol/L within 24 hours of TT (range, 2.11–2.55 mmol/L). Oral Ca ± calcitriol were not routinely given unless adjusted Ca <2.00 mmol/L or patients had symptoms. Under these circumstances, Oscal 1,500–3,000 mg ± calcitriol 0.25 mcg twice daily were prescribed until first clinic visit 1– 2 weeks later. Patients requiring Ca ± calcitriol supplements after their first postoperative visit were followed-up and had their calcium and PTH checked every 4 weeks until they could maintain normocalcemia without supplements (ie, completely weaned off their supplements).12 Laboratory methods. Serum albumin-adjusted Ca and phosphate levels were measured in the hospital laboratory by standard methods using the Roche Diagnostics Modular Analytic system (Roche Diagnostics, Indianapolis, IN). PTH level was measured by Access 2 immunoassay system (Beckman Coulter, Brea, CA), and the inter- and intra-assay CVs were 5.8 and 4.5%, respectively. The normal range for serum PTH level was 1.2–5.7 pmol/L (to convert pmol/L to pg/mL, divide by 0.106). Serum 25-hydroxyvitamin D was measured by using the electrochemiluminescence immunoassay (Elecsys Vitamin D Total assay), and the interand intra-assay CVs were 6.2 and 4.8%, respectively. The measuring range was 3.00–70.0 ng/mL (to convert ng/mL to nmol/L, multiply by 2.496).
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Statistical analysis. For comparison of categorical variables, v2 tests, and Fisher exact tests were used while for comparison of continuous variables, the Mann-Whitney U was used. For correlation between 2 continuous variables, the Pearson correlation test was performed. To improve clinical utility of continuous variables, Youden index was used to calculate the best cut-off value for predicting hypocalcemia. The area under the receiver-operating curve (AUC) was used to measure the predictability. AUC values closer to 1 meant better predictability, whereas values closer to 0.5 meant poorer predictability. The AUCs were compared using the Delong test.13 All statistical analyses were performed using SPSS version 18.0 (SPSS, Chicago, IL) and the STATA software version 13 (STATA, College Station, TX). P < .05 was considered statistically significant. RESULTS Altogether 94 consecutive patients underwent a successful ICGA after a primary TT. Among these 94 patients, 340 PGs were identified and 324 (95.3%) PGs were later confirmed to be PG on histology. Therefore, only 70 (74.5%) patients had 4 identifiable PGs confirmed on histology and were eligible for analysis. None of these patients had parathyroid tissue or gland inadvertently found on the excised thyroid specimen. Five (7.1%) patients underwent PG autotransplantation. Four patients had 1 PG transplanted and another had 2 PGs transplanted. Table I shows the baseline characteristics and perioperative biochemical changes of these 70 patients. Nine (12.9%) patients developed PH, and all except one patient were able to be weaned off Ca ± calcitriol supplements within 4 weeks of operation. That patient was eventually weaned off Ca ± calcitriol supplements 3 months after operation. No patient had permanent PH (ie, >6 months). In terms of the FI of each identified PG relative to its location and glandular appearance, the mean FI of the left lower PGs was significantly less than that of the right upper PGs (97.36 ± 83.46% vs 135.79 ± 88.64%, P = .007) and left upper PGs (97.36 ± 83.46% vs 134.45 ± 101.95%, P = .028). Also, the upper PGs had significantly greater FIs than the lesser PGs (135.12 ± 95.18% vs 113.15 ± 97.06%, P = .025). In terms of glandular appearance and its correlation with FI, among the 274 ISPGs, 143 (52.2%) seemed discolored at the end of operation while the rest (n = 131) remained normal-looking. The FI value between the discolored and normal-looking ISPGs was similar
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Table I. Baseline characteristics and biochemical changes after total thyroidectomy Parameters Age at operation (y) Sex (male:female) Operative indication Benign pathology Graves’ disease/toxic goiter Indeterminate cytology Malignancy Weight of excised gland (g) Total operating time (min) Total time taken for the ICGA (min) Estimated blood loss (mL) No. of patients with 2 ISPGs 3 ISPGs 4 ISPGs No. of patients with No PG auto-transplanted 1 PG auto-transplanted 2 PGs auto-transplanted Preoperative adjusted calcium (mmol/L) Preoperative 25-hydroxyvitamin D3 (ng/mL)* Postoperative day-0 adjusted serum calcium (mmol/L) Postoperative day-1 adjusted serum calcium (mmol/L) No. of patients with postoperative hypocalcemia (adjusted serum calcium #2.00 mmol/L) Adjusted Ca drop from preoperative to postoperative day-0 (%) Adjusted Ca drop from preoperative to postoperative day-1 (%) Preoperative PTH (Pre-PTH) (pmol/L)y Postoperative PTH on postoperative day-0 (PTH-D0) (pmol/L)y Postoperative PTH on postoperative day-1 (PTH-D1) (pmol/L)y
Total no. of patients (n = 70) 54.5 ± 15.0 13:57 38 (54.3) 15 (21.4) 5 (7.1) 12 (17.1) 50.4 ± 48.9 109.1 ± 49.8 2.7 ± 0.5 17.6 ± 14.9 1 (1.4) 4 (5.7) 65 (92.9) 65 (92.9) 4 (5.7) 1 (1.4) 2.32 ± 0.80 47.55 ± 185.40 2.21 ± 0.80 2.16 ± 0.13 9 (15.7)
4.54 ± 3.55 6.12 ± 5.63 9.41 ± 4.78 4.60 ± 3.03 2.50 ± 1.97
*For vitamin D3, multiply ng/mL by 2.496 get nmol/L. yFor PTH, divide pmol/L by 0.106 to get pg/mL. ICGA, Indocyanine green fluorescence angiography; ISPG, in situ parathyroid gland; Ca, calcium; PTH, parathyroid hormone.
(133.45 ± 98.0% vs 121.44 ± 94.16%, P = .479). The FI for normal-looking ISPGs ranged from 12–335 while the ICG for discolored ISPGs ranged from 0–307. There was no normal-looking ISPG with zero uptake while there was one discolored ISPG with zero uptake. In terms of patients, the median (range) greatest FI of each patient was 208.50% (105.00–419.00) while the median
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Fig 3. A diagram showing the relationship between the greatest and average fluorescence intensity and risk of postoperative hypocalcemia; 150% and 85% were optimal cut-off values for greatest and average fluorescence intensity, respectively.
(range) average FI of each patient was 155.80% (55.50–320.00). There were significant correlations between greatest FI and PTH-D0 (r = 0.081, P < .001), greatest FI and PTH-D1 (r = 0.598, P < .001) and greatest FI and % drop in PTH from preoperative to day-0 (r = 0.239, P < .001), but interestingly, not between average FI and PTH-D0 (r = 0.109, P = .371), average PTH-D1 (r = 0.106, P = .384) and average FI and % drop in PTH from preoperative to day-0 (r = 0.115, P = .345). Figure 3 shows the relationship between FI values and PH. When a patient had the greatest FI value >150%, the chance of PH was zero (0/ 59), and when the greatest FI value was # 150%, 9 (81.8%) developed PH. The 2 patients with the greatest FI value #150% that did not develop PH (ie, normocalcemia) had a greatest FI value of 116% and 119%, respectively. Their average FI value were 56.25% and 112.0%, respectively. Similarly, when a patient had the average FI value >109%, the chance of PH was zero (0/40), but when the overall average FI was <109%, 9/30 (30.0%) developed PH. Table II shows the 9 patients who developed temporary PH after TT. Table III compares the test sensitivity, specificity, and predictability (AUC) between various tests using their optimal cut-off value. The greatest FI value (#150% and >150%) had the greatest sensitivity, specificity, and predictability relative to the other tests. As a predictive test, the greatest FI was superior to PTH-D0 (P = .027) and % PTH drop from day0 to 1 (P < .001). Also, although not significant, the greatest FI tended to be superior to the average FI (P = .073).
Table IV shows the results of using a combined greatest and average FI to predict PH. There was no significance difference in the rate of PH between average FI >85% and average # 85% when the greatest FI was # 150% (80.0% vs 83.3%, P = 1.000). DISCUSSION ICG is a safe and inexpensive dye that has been used for a variety of medical conditions.8-10 In thyroid operation, it has been described as a useful contrast agent for PG identification.14 Although one group11 has recently reported using the PINPOINT camera (Novadaq, Mississauga, ON, Canada) to assess perfusion, it does not provide the surgeon a numeric value of the perfusion, and our system does. To our knowledge, this is the first report to use ICG as a potential perfusion marker during thyroid operation. It works based on the principle that an intravascular ICG molecule becomes fluorescent when exposed to light at wavelengths between 750–800 nm and the intensity of this emitted fluorescence (ie, FI) measured by a charge-coupled camera directly reflects the amount of perfusion within that focused area.8-10 As a result, we hypothesized that patients with a greatest FI value in their ISPGs would have greater parathyroid perfusion and residual function and therefore, lesser risk of PH than those with a lesser FI value. Our data confirmed this hypothesis by first showing that there were significant correlations between the greatest FI and PTH-D0 (r = .081, P < .001), greatest FI and PTH-D1 (r = .598, P < .001) and greatest FI and % drop in PTH from preoperative to day-0 (r = 0.239,
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80.00 66.80 94.71 94.07 96.67 91.55 98.10 95.00 82.31 11.00 3.00 3.00 3.00 3.00 3.00 14.00 15.00 8.00 28.51 28.86 9.00 27.00 5.00 6.00 19.00 43.00 17.00 2.00 1.95 1.76 1.92 1.98 1.90 2.00 2.00 1.96 2.24 2.23 2.03 2.12 2.15 2.09 2.28 2.21 2.38 85.25 84.25 61.25 74.75 99.00 108.5 63.50 97.25 50.75 149 148 111 133 146 140 105 129 110 149 69 89 34 101 88 148 0* 111 14 97 23 133 49 86 31 133 146 55 62 124 140 91 79 105 51 75 23 41 107 112 129 42 40 11 110 0 1 0 0 0 0 0 0 0 Indeterminate Benign Graves’ Graves’ Benign Benign Benign Benign Benign
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*Autotransplanted. PG, Parathyroid gland; FI, fluorescence intensity measured on indocyanine green angiography; RU, right upper parathyroid; RL, right lower parathyroid; LU, left upper parathyroid; LL, left lower parathyroid; Ca-D0, calcium on day-0; Ca-D1, calcium on following morning; PTH-D0, PTH taken immediately after operation; PTH-D1, PTH taken on the following morning; preop, preoperative; D0, postoperative day-0.
Age (y)/sex
67/F 37/F 61/F 48/F 58/F 36/F 55/F 45/F 50/F
Greatest Mean Adjusted Ca-D0 Adjusted PTH-D0 PTH-D1 PTH drop from FI value (%) FI value (%) (mmol/L) Ca-D1 (mmol/L) (pmol/L) (pmol/L) preop to D0 (%) LL LU RL RU
FI of PG (%)
No. of PGs transplanted Operative indication
Table II. Summary of the 9 patients who developed postoperative hypocalcemia (ie, serum adjusted calcium # 2.00 mmol/L)
6 Hung-Hin Lang et al
P < .001). Second, when the greatest FI was > 150% (ie, a FI >150% in at least 1 ISPGs), the risk of developing subsequent PH was 0/59 (0.0%) while when the greatest FI was #150% (ie, none of the ISPGs exhibited a FI >150%), the chance of PH was 9/11 (81.8%). Similarly, when the average FI was >109%, the chance of PH was also 0/40 (0.0%). However, it is worth noting that the average FI was less predictive of PH than the greatest FI (AUC 0.81 vs AUC 0.98, P = .073; Table III). Indeed, our data showed that only 30% of patients developed PH when the average FI was <109% while >80% developed PH when the greatest FI was #150%. Even when an optimal cut-off of 85% was used, only 5/10 (50.0%) developed PH when the average FI was # 85%. Interestingly, among those with greatest FI # 150%, the difference in PH risk was not statistically different between those having average FI >85% and those having average FI # 85% (80.0% vs 83.3%, P = 1.00; Table IV). In other words, measuring the average FI did not significantly add to the overall predictability relative to using greatest FI alone. The implication is that perhaps in the future, finding one wellperfused PG (with a FI >150%) at operation might be sufficient in ruling out the subsequent risk of PH. However, given that this is the first report using FI to predict PH, additional studies are required to confirm this finding. Furthermore, the reason why using greatest FI might be more predictive of PH than average FI remains unexplained. We postulate that perhaps having one well-perfused PG (ie, FI >150%) intraoperatively may offer more resistance to the development of PH than having several less-perfused PGs (FI <150%) after TT. Perhaps future studies could focus on how individual PG functions biochemically when the measured FI of a PG is >150% and #150%. Another finding worth highlighting was that the overall predictability (by AUC) in the greatest FI was superior to PTH-D0 (P = .027) and % PTH drop from D0 to D1 (P < .001). This is important given that these latter tests have been used to guide PH management and facilitate early hospital discharge.15,16 Therefore, measuring the FI on ICGA could be an alternative method in predicting PH and facilitating early hospital discharge after TT. Furthermore, given its potential in distinguishing between well-perfused and less well-perfused PGs, it allows the surgeon to decide which of the ISPGs should be autotransplanted or left in situ. Given that visual inspection is subjective and unreliable,6,7 this could become a new tool for selecting
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Table III. Comparison of different tests in predicting postoperative hypocalcemia (PH) Optimal cut-off value* Greatest FI value on ICGA (%) Average FI value on ICGA (%) PTH on day-0 (pmol/L) PTH on day-1 (pmol/L) PTH drop from preoperative to day-0 (%) PTH drop from day-0 to day-1 (%)
#150 #85 #1.5 #3.0 $80.0 $40.0
Sensitivity (%) 9/9 5/9 6/9 9/9 7/9 6/9
(100) (55.6) (66.7) (100) (77.8) (66.7)
Specificity (%)
AUCy
95% CI
59/61 56/61 56/61 23/61 57/61 33/61
0.98 0.81 0.85 0.87 0.96 0.58
0.95–1.00 0.62–0.99 0.73–0.96 0.76–0.99 0.90–1.00 0.38–0.79
(96.7) (91.8) (91.8) (37.7) (93.4) (54.1)
*Determined by the receiver operating characteristic curve and Youden index. yValues closer to 1.00 indicate better predictability, whereas closer to 0.50 indicate poorer predictability. By DeLong test, the greatest FI was more predictive of PH than in the greatest FI was superior to PTH-D0 (P = .027) and % PTH drop from day-0 to 1 (P < .001). ICGA, Indocyanine green angiography; AUC, area under the receiver-operating curve; FI, fluorescence intensity; PTH, parathyroid hormone.
Table IV. Using a combination of greatest FI and average FI measured during ICGA to predict PH
Outcome
Greatest FI > 150 and average FI >85
Greatest FI > 150 and average FI # 85
Greatest FI # 150 and average FI >85
Greatest FI # 150 and average FI #85
Total
No PH* (%) PH* (%) Total
55 (100.0) 0 (0.0) 55
4 (100.0) 0 (0.0) 4
1 (20.0) 4 (80.0) 5
1 (16.7) 5 (83.3) 6
61 (87.1) 9 (12.9) 70
*PH defined as serum adjusted Ca <2.00 mol/L at 24-hour after total thyroidectomy and/or need for oral Ca ± calcitriol supplements to maintain normocalcemia. FI, Fluorescence intensity; PTH, parathyroid hormone.
patients for parathyroid autotransplantation. For example, those PGs with very low FI value could be taken out and autotransplanted while those with FI >150 might be better left in situ (regardless of its appearance). Another potential application would be to perform ICGA immediately after completing the first side of a TT. This would give the surgeon a better idea on the residual parathyroid function in the first completed side before proceeding to the second side of the TT. This approach may prove to be effective in avoiding longer-term PH in the future. However, at this time, more work needs to be done to define an ISPG as being well-perfused or poorly perfused based on the FI value alone. Our data did not find a significant correlation between the naked eye assessment (ie, color change) and ICG assessment (P = .479). One of the interesting findings was the observed differences in FI among the ISPGs. This may have implications in subtotal parathyroidectomy where perhaps, the one with the greatest FI might be the preferred remnant over the other ISPGs with lower FI.11 In terms of costs, after including the maintenance cost of the SPY imaging system and consumables (including nonreusable plastic drape and
ICG dye) used during the procedure, one ICGA cost around US $253. This is roughly twice the cost of a PTH test (US $120) at our institution. However, given its potential in better selecting patients for parathyroid auto-transplantation and possibly reducing longer-term PH, it may be a costeffectiveness tool. It is worth highlighting that the ICGA is not a perfect predictive tool as there were 2 (2.9%) patients with low FIs who did not develop PH. One patient, in fact, had an average FI of 56.25% and a greatest FI of 119%. For these 2 patients, measurement errors were possible. Furthermore, despite these findings, there were several shortcomings with the present study. First, because this was a single institution study conducted by one surgeon, its applicability in other centers remains unconfirmed. Second, due to the small number of patients and events (such as permanent PH), our study was prone to type II error and it remains unknown how ICGA may affect rate of PH in the longer-term. Third, it should be noted that biopsying all 4 PGs during TT was simply done for the purpose of the study and given the high rate of concordance between visual identification and histology (95.3%), in the future we would proceed to the ICGA without biopsy. However, given that
ARTICLE IN PRESS 8 Hung-Hin Lang et al
biopsy was done in the present study, the FI value might be different from that without the biopsy. Discolored and normal-looking ISPGs had similar FI values on ICGA (133.45 ± 98.0% vs 121.44 ± 94.16%, P = .479). Given that no patients with the greatest FI >150% or average FI >109% developed PH, the ICGA may be a promising operative adjunct in determining residual parathyroid function and predicting the risk of PH. In terms of future applications, this new tool may have a role in selecting patients for parathyroid autotransplantation and guiding surgeons in their approach to the second side of a TT. We would like to thank Dr Tony Shek and his team of pathologists for carefully examining all the excised thyroid specimens during this study period.
REFERENCES 1. Edafe O, Antakia R, Laskar N, Uttley L, Balasubramanian SP. Systematic review and meta-analysis of predictors of post-thyroidectomy hypocalcaemia. Br J Surg 2014;101: 307-20. 2. Lorente-Poch L, Sancho JJ, Mu~ noz-Nova JL, SanchezVelazquez P, Sitges-Serra A. Defining the syndromes of parathyroid failure after total thyroidectomy. Gland Surg 2015;4: 82-90. 3. Wong KP, Lang BH. Graves’ ophthalmopathy as an indication increased the risk of hypoparathyroidism after bilateral thyroidectomy. World J Surg 2011;35:2212-8. 4. Mehanna HM, Jain A, Randeva H, Watkinson J, Shaha A. Postoperative hypocalcemia---the difference a definition makes. Head Neck 2010;32:279-83. 5. Johansson K, Ander S, Lennquist S, Smeds S. Human parathyroid blood supply determined by laser-Doppler flowmetry. World J Surg 1994;18:417-20; discussion 420-1. 6. Kuhel WI, Carew JF. Parathyroid biopsy to facilitate the preservation of functional parathyroid tissue during thyroidectomy. Head Neck 1999;21:442-6. 7. Lang BH, Chan DT, Chow FC, Wong KP, Chang RY. The association of discolored parathyroid glands and hypoparathyroidism following total thyroidectomy. World J Surg 2016;40:1611-7. 8. Taylor SR, Jorgensen JB. Use of fluorescent angiography to assess donor site perfusion prior to free tissue transfer. Laryngoscope 2015;125:E192-7. 9. Matsui A, Winer JH, Laurence RG, Frangioni JV. Predicting the survival of experimental ischaemic small bowel using intraoperative near-infrared fluorescence angiography. Br J Surg 2011;98:1725-34. 10. Braun JD, Trinidad-Hernandez M, Perry D, Armstrong DG, Mills JL Sr. Early quantitative evaluation of indocyanine green angiography in patients with critical limb ischemia. J Vasc Surg 2013;57:1213-8. 11. Vidal Fortuny J, Belfontali V, Sadowski SM, Karenovics W, Guigard S, Triponez F. Parathyroid gland angiography with indocyanine green fluorescence to predict parathyroid function after thyroid surgery. Br J Surg 2016;1035:537-43. 12. Lang BH, Wong KP. How useful are perioperative biochemical parameters in predicting the duration of calcium and/
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DISCUSSION Dr Richard A. Prinz (Evanston, IL): Brian, a very, very nice study. I have a number of questions. Now, you biopsied all of your glands and you only used this technique according to your protocol when four glands were identified. So do you think biopsy is necessary? And what do you do if you have not identified all four glands? Is it still a useful technique? And then it seems like you are using this for a method to determine if you need to autotransplant a gland. Did your rate or the number of parathyroid autotransplantations increase with this technique compared to what your historical rates were? Thank you. Dr Brian H. Lang: For your first question related to the biopsy, this was done basically for the study because we want to make sure that what we are seeing was a parathyroid gland and it was not something else like a lymph node or a thyroid nodule. For your second question, the rate of autotransplantation actually has been the same as before. It is around 5% for our own series, before and after the study. So we have not increased the autotransplant rate, and that is because the principle of autotransplantation has not really changed. Basically, if we see a gland that has a vascular pedicle, we would leave it in situ. We will not autotransplant it. Dr Samuel K. Snyder (Temple, TX): Thank you for a very interesting study. You have given us a new concept for evaluating adequate vascularity of the parathyroid intraoperatively. I just have 2 quick questions. One is, a common problem is hematoma on the parathyroid. And my question is, does the development of a hematoma or a bruising on the surface of the parathyroid, not necessarily ischemia but bruising, affect your fluorescence levels?
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Secondly, did you introduce a control mechanism? Because most of us when we do parathyroid surgery, we look at the parathyroids and we say, you know, they look good. I do not think this patient is going to have a problem postop. You had the option of doing that before you did your fluorescence and then compare the surgeon’s perception as to what the vascularity was going to be and then whether or not the technique actually introduced extra information that helped you. Dr Brian H. Lang: Essentially when we compared---first of all, visual inspection could be very subjective. Something that is discolored for you may be different for another surgeon. Essentially, all the procedures were done by me. Essentially, I compared the fluorescence intensity of a discolored gland, which could or could not have a hematoma, and also a normal-looking gland. Essentially we found there was no statistical significance in the fluorescence intensity between the normal-looking and the bruised gland. So it probably supports your concept that probably these bruised glands are actually just bruised and they are not ischemic. Dr Janice L. Pasieka (Calgary, AB): Brian, wonderful presentation. Could you comment on how you got this through ethics? If we go back to the days of a 4 gland exploration, we know that by biopsying all of our normal glands, or the remaining 3 normal glands, increased the rate of hypocalcemia postoperatively. So how did you get that through ethics? My second question is, you are an experienced endocrine surgeon. You know what a parathyroid looks like most of the time. Have you now moved to not biopsying it and using this technique in your practice day to day? Dr Brian H. Lang: Basically, it was not a large biopsy. It was a shaving of the capsule of the gland. So we do not think that that actually induces iatrogenic hypocalcemia. Also, the reason for doing biopsy was because sometimes it is very difficult to know whether it is a real para or not. If you look at our data more closely, there is a 93% concordance. So we are correct probably 9 out of 10 times. But having said that, there was still a 10% difference, and that is the reason for doing the biopsy. We do not routinely biopsy a parathyroid gland, but for this study, we did.
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Dr Quan-Yang Duh (San Francisco, CA): Brian, wonderful study. And conceptually I looked at this test very similar to neuromonitoring. And when we do neuromonitoring, you know, people argue about whether or not we need it or do not need it. This is the other complication that we all dread for patients with thyroidectomy. The difference is in neuromonitoring you can do it, do your operation, repeat it, do your operation, et cetera, or you can do continuous monitoring. The question I have for you is, how often can you do the injection? So I inject it once. I looked at the thing. How many minutes do I have to wait? Can I do another one? Dr Brian H. Lang: It has a half-life, so you can repeat every 30 minutes. So you can do it before you remove the thyroid gland and do it after the operation. You can do it a couple of times. It does not matter. It gets washed out pretty quickly. Dr Quan-Yang Duh (San Francisco, CA): So give me an example of a case that you do. How many times do you inject indocyanine green? Dr Brian H. Lang: For this study, we only inject once. It was immediately after the total thyroidectomy. But potentially this could be done several times. So you can complete one side of the total thyroidectomy and you can do the ICG on that side and see the 2 parathyroid glands before you proceed to the opposite side. So this is an advantage. Dr Quan-Yang Duh (San Francisco, CA): So there is no issue of toxicity? Dr Brian H. Lang: No. Dr James G. Norman (Tampa, FL): I think it is important to note against the conversation that is happening here, it is really important to differentiate between thyroid surgery and parathyroid surgery. I agree with Dr Pasieka, what she says about biopsying parathyroid glands during thyroid surgery. I do not see much role in that. But we have to clarify this age-old adage that biopsying of parathyroid glands, like during parathyroid surgery, has an increased effect on hypoparathyroidism, hypocalcemia. It is nonsense. We cannot continue that type of nonsense. We biopsy all 4 parathyroid glands in every patient and have done so for decades. Absolutely does not cause hypoparathyroidism.
ARTICLE IN PRESS 10 Hung-Hin Lang et al
Indocyanine green fluorescence angiography for quantitative evaluation of in situ parathyroid gland perfusion and function after total thyroidectomy Brian Hung-Hin Lang, MS, FRACS, Carlos K. H. Wong, PhD, Hing Tsun Hung, MBBS, MRCS, Kai Pun Wong, MBBS, FRCS, Ka Lun Mak, MBBS, MRCS, and Kin Bun Au, MBBS, FRCS, Hong Kong SAR, China A total of 70 patients underwent intraoperative indocyanine green angiography after total thyroidectomy. Our data showed that indocyanine green angiography is a promising operative adjunct for predicting biochemical hypocalcemia after total thyroidectomy.
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