Thallium-pertechnetate subtraction scanning in the preoperative localization of an ectopic undescended parathyroid gland

Although bilateral exploration is highly effective in the treatment of primary hyperparathyroidism, minimally invasive parathyroidectomy has evolved into the procedure of choice when a single parathyroid lesion can be localized preoperatively. In this article, we discuss the utilization of thallium-pertechnetate subtraction scanning (TPSS) after technetium Tc-99m sestamibi scintigraphy failed to localize an ectopic parathyroid adenoma. Subsequently, radioguided resection of an undescended parathyroid adenoma inferior to the left submandibular gland was performed with surgical cure after a single procedure. This case report illustrates the importance of TPSS as a second-line modality in preoperative adenoma localization, thereby using minimally invasive techniques to successfully treat this patient's primary hyperparathyroidism.     

Enhanced scintigraphic protocol required for optimal preoperative localization before targeted minimally invasive parathyroidectomy

At our tertiary care institution, a targeted minimally invasive parathyroidectomy (MIP) is the preferred surgical procedure for primary hyperparathyroidism. Similar to unilateral neck exploration (UNE), preoperative scintigraphic localization of the adenoma in relation to the midline is required. However, in contrast to the abbreviated standard incision for UNE, 2 distinct incision sites, 1 medial and 1 lateral, are available on each side with MIP. The incision site is ultimately chosen based on scintigraphic determination of the adenoma's vascular origin to facilitate ligation and removal. Unfortunately, the scintigraphic location of a parathyroid adenoma does not necessarily reflect the site of its vascular origin. We reviewed our database to identify factors that accurately predict the site of vascular origin of parathyroid adenomas. A retrospective chart review was performed on 125 patients who underwent Tc-99m sestamibi scintigraphy and parathyroidectomy. Scintigraphic localization, surgical findings, and histopathology were recorded. Preoperative image interpretations that were discordant with operative findings were independently reviewed. Scintigraphy identified the presence of an adenoma in 105 of 118 patients (89%) with primary hyperparathyroidism. In 17 of the 105 cases (16%), the scintigraphic interpretation did not accurately reflect the site of superior or inferior vascular origin seen at surgery. In many discordant cases, anterior images were insufficient for determining the vascular origin. The posterior displacement of an adenoma in relation to the thyroid on early lateral images was often critical in determining the superior or inferior vascular origin. Scintigraphic determination of the superior or inferior vascular origin of a parathyroid adenoma directs incision placement for MIP. Imaging protocols should include early lateral images when localizing parathyroid adenomas before minimally invasive parathyroidectomy.     

Preoperative localization and radioguided parathyroid surgery.

Clinical or subclinical hyperparathyroidism is one of the most common endocrine disorders. Excessive secretion of parathyroid hormone is most frequently caused by an adenoma of >or=1 parathyroid gland. Unsuccessful surgery with persistent hyperparathyroidism, due to inadequate preoperative or intraoperative localization, may be observed in about 10% of patients. The conventional surgical approach is bilateral neck exploration, whereas minimally invasive parathyroidectomy (MIP) has been made possible by the introduction of (99m)Tc-sestamibi scintigraphy for preoperative localization of parathyroid adenomas. In MIP, the incision is small, dissection is minimal, postoperative pain is less, and hospital stay is shorter. Localization imaging techniques include ultrasonography, CT, MRI, and scintigraphy. Parathyroid scintigraphy with (99m)Tc-sestamibi is based on longer retention of the tracer in parathyroid than in thyroid tissue. Because of the frequent association of parathyroid adenomas with nodular goiter, the optimal imaging combination is (99m)Tc-sestamibi scintigraphy and ultrasonography. Different protocols are used for (99m)Tc-sestamibi parathyroid scintigraphy, depending on the institutional logistics and experience (classical dual-phase scintigraphy, various subtraction techniques in combination with radioiodine or (99m)Tc-pertechnetate). MIP is greatly aided by intraoperative guidance with a gamma-probe, based on in vivo radioactivity counting after injection of (99m)Tc-sestamibi. Different protocols used for gamma-probe-guided MIP are based on different timing and doses of tracer injected. Gamma-probe-guided MIP is a very attractive surgical approach to treat patients with primary hyperparathyroidism due to a solitary parathyroid adenoma. The procedure is technically easy, safe, with a low morbidity rate, and has better cosmetic results and lower overall cost than conventional bilateral neck exploration. Specific guidelines should be followed when selecting patients for gamma-probe-guided MIP.     

Comparison between 99mTc-tetrofosmin/pertechnetate subtraction scintigraphy and 99mTc-tetrofosmin SPECT for preoperative localization of parathyroid adenoma in an endemic goiter area

RATIONALE AND OBJECTIVES: Technetium-99m-((99m)Tc-) tetrofosmin, a cationic, lipophilic complex like (99m)Tc-sestamibi, has proved to be a potential tracer for parathyroid scintigraphy despite some differences in washout behavior from the thyroid gland. Previous results comparing a double-phase technique with single-proton emission computed tomography (SPECT) or with subtraction techniques demonstrated a high detection rate, especially when SPECT and subtraction techniques were used, whereas the double-phase protocol revealed only moderate results. In this study, a direct comparison was made between (99m)Tc-tetrofosmin/pertechnetate subtraction and SPECT to elucidate the optimal protocol for tetrofosmin parathyroid imaging. METHODS: Twenty-three patients who were biochemically suspected of parathyroid adenoma or hyperplasia due to primary or tertiary hyperparathyroidism were included in our study. In all patients, serum calcium, phosphate, and intact parathormone levels were analyzed in a single blood sample before (99m)Tc-tetrofosmin/pertechnetate subtraction scintigraphy and SPECT. Ultrasound of the neck was performed in all patients to exclude false-positive results due to thyroid adenomas. All patients underwent parathyroidectomy with intraoperative revision of all parathyroid glands, and the histological results were compared with preoperative findings. RESULTS: Both imaging modalities, ie, subtraction scintigraphy and SPECT, correctly identified 20 of 23 (87%) histologically confirmed adenomas preoperatively. The positive predictive value was calculated to be 95% and 100%, respectively, for these two methods. Subtraction scintigraphy and SPECT showed concordant results in 19 patients (18 positive, 1 false-negative) and discordant results in 4 patients (2 positive with subtraction, 2 with SPECT). The combined use of subtraction scintigraphy and SPECT techniques revealed a sensitivity of 95.7% (22/23) and a positive predictive value of 95%. The whole procedure can be performed in less than 90 minutes per patient. Whereas subtraction scintigraphy tended to show more false-positive retentions due to thyroid adenomas, the interpretation of SPECT may be difficult in small adenomas with missing thyroid/parathyroid differential washout. CONCLUSIONS: Both imaging modalities, subtraction scintigraphy with pertechnetate and SPECT, are highly sensitive methods for parathyroid adenoma localization with (99m)Tc-tetrofosmin. However, our study did demonstrate that a combination of both modalities can further improve the diagnostic accuracy. Especially in an endemic goiter area, additional ultrasound may be required to avoid false-positive results due to thyroid adenomas.     

Radioguided surgery in primary hyperparathyroidism

Surgical neck exploration is usually made in primary hyperparathyroidism (PHPT). Localization of the adenoma or detection of hyperplasia may reduce the operation period and limit the extent of the surgery. In this study the effficacy of preoperative Tc-99m MIBI scintigraphy and intraoperative gamma probe was evaluated. MATERIALS AND METHODS: Six patients with PHPT had preoperative Tc-99m MIBI parathyroid scintigraphy and intraoperative gamma probe (IGP) was used in surgical neck exploration. RESULTS: Parathyroid adenoma was observed in 2/6 patients on scintigraphy in the right retroclavicular region and the left lobe of the thyroid. Both of them were clearly detected by IGP during the surgery and easily removed by the surgeon in a short time (35 min) with a small incision. Pathologic examination confirmed the parathyroid adenoma. No abnormal MIBI uptake was not observed in scintigraphy in 4/6 patients. Subtotal parathyroidectomy was performed in these patients. CONCLUSION: Preoperative Tc-99m MIBI scintigraphy and the use of IGP may limit the exploration and also the operation time and reduce surgical complications.     

Technetium-99m pertechnetate uptake in ectopic parathyroid adenoma

A 37-year-old male with a persistent increased parathyroid hormone level, after subtotal thyroidectomy and parathyroidectomy, was referred for scintigraphic localization of a possible ectopic parathyroid adenoma. Tc-99m pertechnetate and Tc-99m MIBI scintigraphy were performed on separate days. There was marked uptake of both tracers in the mediastinum, which at surgery was confirmed to be an extrathyroidal parathyroid adenoma. Hypervascularity was suggested as a possible explanation for rare cases of pertechnetate avid parathyroid adenomas. And Tc-99m MIBI scintigraphy proved to be a successful imaging procedure for ectopic parathyroid tissue.     

Can thallium-pertechnetate subtraction scanning play a role in the preoperative imaging for minimally invasive parathyroidectomy?

PURPOSE: Preoperative Tc-99m sestamibi scanning can identify candidates for minimally invasive parathyroid surgery. However, a significant number of patients with single gland disease have negative scans and are not considered for the minimally invasive procedure. MATERIALS AND METHODS: To determine if T1-201/Tc-99m sodium pertechnetate subtraction scanning (TPSS) is a viable alternative imaging technique for patients with primary hyperparathyroidism (1 degrees HPTH), we reviewed our experience. The outcomes of 100 consecutive patients with 1 degrees HPTH who underwent preoperative TPSS and parathyroid exploration between 1995 and 2000 at our institution were retrospectively reviewed. RESULTS: The mean preoperative calcium and parathyroid hormone levels were 10.8 mg/dL and 220 pg/mL, respectively. The overall cure rate was 96%. Single gland disease was present in 88%. Of the 100 patients studied, 15 underwent both a Tc-99m sestamibi scan and TPSS, whereas the other 85 had only the TPSS. CONCLUSIONS: The sensitivity and positive predictive value of the TPSS were 73.3% and 90.4%, respectively. In the patients undergoing both TPSS and Tc-99m sestamibi scans, the results concurred in 60%. However, in 20% of the remaining patients, TPSS correctly localized the abnormal parathyroid(s) when Tc-99m sestamibi failed. TPSS has a comparable sensitivity and positive predictive value to Tc-99m sestamibi scanning. In patients with a negative Tc-99m sestamibi scan, TPSS can provide additional localizing information. As a result of the high positive predictive value of TPSS, a single parathyroid gland localized by TPSS alone can then be approached by minimally invasive parathyroidectomy.     

Diagnostic dilemmas in parathyroid scintigraphy.

PURPOSE: Tc-99m MIBI scintigraphy can be useful for preoperative localization of parathyroid adenomas, despite its limited sensitivity. To refine interpretation, the authors conducted prospective reviews of the scintigraphic studies of patients with concomitant thyroid nodular disease and revised the false-negative and false-positive results. MATERIALS AND METHODS: Seventy-seven patients with primary hyperparathyroidism, associated with a solitary parathyroid adenoma, underwent dual-phase MIBI scintigraphy with subsequent injection of Tc-99m pertechnetate before surgery. The false-negative and false-positive scintigraphic findings were identified and revised. RESULTS: After surgery, revision of 19 false-negative scans of the total 77 studies led to the demonstration of an adenoma in seven patients. In five of the seven studies, the adenoma had been overlooked as a result of rapid tracer washout. Two additional small focal lesions would have also been identified if subtraction had been used for differences in contour of the MIBI and pertechnetate images. Four studies were interpreted falsely as abnormal, leading to a positive predictive value of 91%; three were associated with thyroid nodular disease. CONCLUSIONS: Differential washout of MIBI from thyroid and parathyroid tissue is not universal. When MIBI is washed out rapidly from parathyroid adenomas, subtraction of a thyroid image should be performed and differences in contour delineated to localize the adenoma accurately. Some, but not all, thyroid lesions account for the false-positive findings.     

Incremental diagnostic value of preoperative 99mTc-MIBI SPECT in patients with a parathyroid adenoma.

The purpose of this prospective study was to evaluate the diagnostic value of early parathyroid SPECT combined with quantitative analysis as compared with planar imaging in patients undergoing minimally invasive radioguided surgery. METHODS: A total of 52 consecutive patients with primary hyperparathyroidism underwent planar and SPECT parathyroid scintigraphy 2-5 d before surgery. Each patient had a single-tracer dual-phase technique using (99m)Tc-methoxyisobutylisonitrile ((99m)Tc-MIBI) and a double-tracer subtraction technique using a delayed (99m)Tc-pertechnetate scan. Immediately after the first (99m)Tc-MIBI planar image, a SPECT study was acquired. Before radioguided parathyroidectomy, each patient was reinjected with (99m)Tc-MIBI. Serum calcium levels were available for all patents before surgery and at 8 and 24 h after surgery. Serum parathyroid hormone (PTH) levels were also available for all patients. Quantitative analysis was performed using the average count ratio of parathyroid to left thyroid lobe, right thyroid lobe, and maximum thyroid activity. All patients had histopathologic examination of the removed glands. RESULTS: The average time for radioguided surgery was 30 min (range, 20-40 min). Postsurgical calcium levels correlated significantly with the adenoma weight (r = 0.5; P = 0.016). Combined planar scintigraphy correctly identified 41 adenomas (79%). SPECT increased the sensitivity to 96%. SPECT was superior to planar imaging in 9 patients, mainly in patients with ectopic adenomas or with multinodular goiters. Gland size did not affect significantly the detectability of SPECT. (99m)Tc-MIBI retention was noted in only 31 adenomas (60%). The average uptake ratios of parathyroid counts to the left lobe, right lobe, and maximum thyroid activity were 1.20 +/- 0.42, 1.29 +/- 0.45, and 0.84 +/- 0.35, respectively. The latter ratio was significantly correlated with PTH levels before surgery (r = 0.408; P = 0.04). CONCLUSION: Our data indicate that early preoperative SPECT in patients with primary hyperparathyroidism is essential for accurate localization of parathyroid adenomas and for the selection of patients who are candidates for minimally invasive radioguided surgery. Planar parathyroid imaging is less sensitive compared with SPECT, and washout kinetics of (99m)Tc-MIBI are unreliable in the dual-phase technique. Patients with higher presurgical PTH levels may especially benefit from radioguided surgery.     

Clinical role of 99mTcO4/MIBI scan, ultrasound and intra-operative gamma probe in the performance of unilateral and minimally invasive surgery in primary hyperparathyroidism

The main purposes of this study were: (a) to investigate the efficacy of an imaging protocol based on the combination of 99mTcO4/MIBI scintigraphy and neck ultrasound (US) in selecting patients with primary hyperparathyroidism (HPT) for unilateral neck exploration, and (b) to help define the role of the intraoperative MIBI gamma probe (IMGP) technique in the performance of minimally invasive radio-guided surgery (MIRS). One hundred and forty-three consecutive patients with primary HPT were enrolled in the study. We used a modified 99mTcO4/MIBI scintigraphic procedure which included the oral administration of potassium perchlorate to cause rapid 99mTcO4 washout from the thyroid tissue, thereby permitting the acquisition of high-quality early MIBI images. A single-photon emission tomography (SPET) acquisition was also obtained in 21 patients, of whom seven had an enlarged parathyroid gland (EPG) in the mediastinum at planar scintigraphy and 14 had discordant scan/US findings for the presence of a cervical EPG. Neck US was performed in the same session as scintigraphy using a small-parts, high-resolution 10-MHz transducer. All patients were then operated on by the same surgical team. Quick PTH assay (QPTH) was used to measure PTH intraoperatively to confirm successful parathyroidectomy. In patients with scan/US evidence of a solitary EPG and with a normal thyroid gland, limited, unilateral neck surgery or, more recently, MIRS was planned (n=91). In patients with scan/US evidence of multiglandular disease (MGD) (n=21) or concomitant nodular goitre (n=24) or in patients with a negative scan/US evaluation (n=7), extensive bilateral neck exploration was planned (n=52). In 87 of the 91 patients (95.6%) in whom preoperative imaging indicated the presence of a solitary EPG and a normal thyroid gland, a single parathyroid adenoma was found at surgery, and these patients were treated by unilateral neck exploration or MIRS. In the remaining four patients of this group, conversion to bilateral neck exploration was required because parathyroid carcinoma (n=3) or MGD (n=1) was diagnosed at operation. In some cases SPET was helpful in better localising the EPG. In particular, in 5 of the 21 patients evaluated, SPET localised an EPG deep in the neck or mediastinum and at surgery a parathyroid adenoma was found in the paratracheal or para-oesophageal space. In 43 of the 46 patients (93.5%) who were candidates for MIRS, the IMGP technique allowed parathyroidectomy to be performed through a small, 2- to 2.5-cm skin incision with a short duration of intervention (mean 34 min). We conclude that: (a) The integrated scan/US imaging protocol that we used appears to be accurate in selecting patients with primary HPT for unilateral neck exploration. (b) In our series the most prevalent cause of bilateral neck exploration was the co-existence of a nodular goitre; thus accurate preoperative evaluation of the thyroid gland by dual-tracer scintigraphy and US imaging is strongly recommended in all patients with HPT. (c) SPET can provide the surgeon with useful information when an EPG is located deep in the neck or mediastinum. (d) IMGP appears to be a useful intraoperative device in HPT patients with solitary parathyroid adenomas and a normal thyroid gland, since it permits minimally invasive and time-saving surgery.     

Diagnosis of hyperparathyroidism

AIM: To preoperatively localize enlarged parathyroid glands in patients with hyperparathyroidism (HPT). METHODS: Besides clinical and biochemical workup, high-resolution ultrasonography (US) is the most commonly used imaging method.Additionally,Tc-99m-MIBI scintigraphy in subtraction or biphasic technique, computed tomography (CT) and magnetic resonance imaging (MRI) are used. RESULTS: US fails to detect a minimum of 10% of enlarged parathyroid glands,most commonly due to ectopic location, or difficult examination conditions, such as nodular goiter or previous surgery. If attempted US localization is unsuccessful, multiphase scintigraphy, using Tc-99m-sestamibi, can help to locate ectopic adenomas in the mediastinum. With SPECT, ademomas can be found which escape detection on planar scans due to their small size.With combined use of US and scintigraphy, a correct localization of parathyroid adenomas is possible in up to 90%. CT and MRI are of limited value due to their low specificity. CONCLUSION: For newly diagnosed hyperparathyroidism, high-resolution US is the method of choice for localizing parathyroid adenomas.If ultrasound fails to detect a lesion, Tc-99m-MIBI scintigraphy is recommended. In patients scheduled for re-operation for recurrent or persistent HPT, a preoperative detection of a parathyroid adenoma should be attempted whenever possible, in order to minimize the extent of surgery. The role of CT or MRI is mainly to help to better anatomically localize a suspected adenoma previously detected with scintigraphy.     

Correlation between P-glycoprotein (P-gp) expression in parathyroid and Tc-99m MIBI parathyroid image findings

The major factor to influence localization of parathyroid adenomas is tumor size. P-glycoprotein (P-gp) expression in parathyroid adenomas has been considered to be an another possible factor to influence localization of parathyroid adenomas because false-negative studies have been reported with large tumors and true-positives reported with very small tumors in previous studies. The aim of this study was to characterize Tc-99m MIBI uptake and retention by parathyroid adenomas and to correlate this with cell surface expression of P-gp. Sixteen patients with parathyroid adenoma (larger than 1.5 gm) underwent dual-phase (10min and 2hr) Tc-99m MIBI parathyroid image immediately before parathyroid exploration. Tissues were obtained from normal and abnormal parathyroid glands and from the thyroid gland. Immunohistochemistry (IHC) was obtained with monoclonal antibodies to identify P-gp expression in all tissues. All of the 16 parathyroid adenomas and 32 normal control specimens (16 normal parathyroid and 16 normal thyroid specimens) were submitted for P-gp detection by IHC. The dual-phase Tc-99m MIBI parathyroid image accurately localized 14 parathyroid adenomas, but not the remaining 2 adenomas. The 14 parathyroid adenomas with significant Tc-99m MIBI uptake in delayed 2hr images revealed negative P-gp expression, but the 2 adenomas without significant Tc-99m MIBI uptake, as well as normal parathyroid and normal thyroid specimens, revealed positive P-gp expression when evaluated by IHC. Not only the size of parathyroid adenomas, but also significant P-gp expression limited the sensitivity of dual-phase Tc-99m MIBI parathyroid image to localize parathyroid adenomas before operation.     

'Shine through' on dual tracer parathyroid scintigraphy: a potential pitfall in interpretation

Dual tracer scintigraphy has become the procedure of choice for preoperative localization of parathyroid adenomas. The typical protocol used by most laboratories is to initially perform a Tc-99m sestamibi (MIBI) study with early and delayed (2-3 hours) washout phase images. This is followed by a thyroid-specific Tc-99m pertechnetate study. A potential pitfall exists if the delayed phase of the initial MIBI study shows an intense, abnormal focus of retention. This focus may interfere with interpretation of the subsequent pertechnetate study because of a "shine through" effect. To differentiate a parathyroid adenoma from a thyroid adenoma, it may be necessary to repeat the thyroid-specific pertechnetate scan on a separate day after the dual tracer study.     

Minimally invasive radioguided parathyroidectomy for hyperparathyroidism

Clinical or subclinical hyperparathyroidism (HPT) is one of the most common endocrine disorders. In patients with HPT who meet the indications for parathyroidectomy, complete surgical resection of all hyperfunctioning parathyroid tissue is essential for the curative treatment. The conventional surgical approach is bilateral neck exploration, whereas minimally invasive parathyroidectomy has been made possible by the introduction of ^99mTc-sestamibi scintigraphy for preoperative localization of parathyroid adenomas. In minimally invasive surgery, the surgeon expects some modalities that predict complete resection of all hyperfunctioning parathyroid glands. The prevalence rate of ^99mTc-sestamibi scanning for single parathyroid adenoma was widely accepted as 85–95%. Moreover, the recent developing technology of semiconductor electronics has produced useful portable γ-probes. Intraoperative navigation using these devices provides the possibility of easy and definitive identification of parathyroid nodules during the operation. In minimally invasive radioguided parathyroidectomy using γ-probe, different protocols are based on different timing and doses of tracer injected. Each procedure is technically easy, safe, with a low morbidity rate, and has better cosmetic results and lower overall cost than conventional bilateral neck exploration. We have applied this technique in selected patients and achieved success comparable to that achieved with contemporaneously performed standard neck exploration. In the hands of a competent surgeon, the use of sestamibi scanning and radioguided parathyroidectomy in appropriately selected patients is a useful technique.     

The usefulness of Tc-99m tetrofosmin scintigraphy in the diagnosis and localization of hyperfunctioning parathyroid glands

PURPOSE: The aim of the work was to study the diagnostic value of Tc-99m tetrofosmin to localize anomalous parathyroid glands in patients with hyperparathyroid disease. METHODS: We studied 31 patients, 19 with primary and 12 with secondary hyperparathyroid disease. Five of these patients were renal graft recipients. All patients underwent surgery. Each patient was injected with 555 to 740 MBq (15 to 20 mCi) Tc-99m tetrofosmin. Subsequently, radionuclide images were acquired 15 and 120 minutes after injection using a low-energy, all-purpose, parallel-hole collimator. Pertechnetate thyroid scintigraphy was obtained in nine cases (24 to 48 h later) when the thyroid activity made it difficult to identify the parathyroid glands. RESULTS: All cases showed tracer uptake as early as 15 minutes after injection. In the group of patients with primary hyperparathyroid disease, 15 showed focal uptake in a parathyroid gland, and surgery revealed an adenoma in the same location. In one patient with hyperplasia, scintigraphy identified only two of four diseased glands. In the three remaining cases, scintigraphy showed focal uptake in the lower parathyroid gland, whereas at surgery the abnormal gland was located in the upper pole. In the secondary hyperparathyroidism group, seven patients showed diffuse tracer uptake in two or more glands, and histologic analysis confirmed hyperplasia in all of them. Five cases showed focal uptake, with three evaluated after surgery (uptake in the only remaining gland); one of them was a renal graft recipient, and the remaining patient had chronic renal failure and was receiving hemodialysis. CONCLUSIONS: Our results suggest that Tc-99m tetrofosmin may be a suitable tracer for preoperative detection and screening of anomalous parathyroid glands. The earlier images at 15 minutes were better than those at 120 minutes. Tc-99m tetrofosmin is cleared more slowly from the normal thyroid than is Tc-99m sestamibi, and both of these tracers may give better results than the old pertechnetate TI-201 subtraction technique.     

Clinical role of 99mTcO4/MIBI scan, ultrasound and intra-operative gamma probe in the performance of unilateral and minimally invasive surgery in primary hyperparathyroidism

The main purposes of this study were: (a) to investigate the efficacy of an imaging protocol based on the combination of ^99mTcO₄/MIBI scintigraphy and neck ultrasound (US) in selecting patients with primary hyperparathyroidism (HPT) for unilateral neck exploration, and (b) to help define the role of the intraoperative MIBI gamma probe (IMGP) technique in the performance of minimally invasive radio-guided surgery (MIRS). One hundred and forty-three consecutive patients with primary HPT were enrolled in the study. We used a modified ^99mTcO₄/MIBI scintigraphic procedure which included the oral administration of potassium perchlorate to cause rapid ^99mTcO₄ washout from the thyroid tissue, thereby permitting the acquisition of high-quality early MIBI images. A single-photon emission tomography (SPET) acquisition was also obtained in 21 patients, of whom seven had an enlarged parathyroid gland (EPG) in the mediastinum at planar scintigraphy and 14 had discordant scan/US findings for the presence of a cervical EPG. Neck US was performed in the same session as scintigraphy using a small-parts, high-resolution 10-MHz transducer. All patients were then operated on by the same surgical team. Quick PTH assay (QPTH) was used to measure PTH intraoperatively to confirm successful parathyroidectomy. In patients with scan/US evidence of a solitary EPG and with a normal thyroid gland, limited, unilateral neck surgery or, more recently, MIRS was planned (n=91). In patients with scan/US evidence of multiglandular disease (MGD) (n=21) or concomitant nodular goitre (n=24) or in patients with a negative scan/US evaluation (n=7), extensive bilateral neck exploration was planned (n=52). In 87 of the 91 patients (95.6%) in whom preoperative imaging indicated the presence of a solitary EPG and a normal thyroid gland, a single parathyroid adenoma was found at surgery, and these patients were treated by unilateral neck exploration or MIRS. In the remaining four patients of this group, conversion to bilateral neck exploration was required because parathyroid carcinoma (n=3) or MGD (n=1) was diagnosed at operation. In some cases SPET was helpful in better localising the EPG. In particular, in 5 of the 21 patients evaluated, SPET localised an EPG deep in the neck or mediastinum and at surgery a parathyroid adenoma was found in the paratracheal or para-oesophageal space. In 43 of the 46 patients (93.5%) who were candidates for MIRS, the IMGP technique allowed parathyroidectomy to be performed through a small, 2- to 2.5-cm skin incision with a short duration of intervention (mean 34 min). We conclude that: (a) The integrated scan/US imaging protocol that we used appears to be accurate in selecting patients with primary HPT for unilateral neck exploration. (b) In our series the most prevalent cause of bilateral neck exploration was the co-existence of a nodular goitre; thus accurate preoperative evaluation of the thyroid gland by dual-tracer scintigraphy and US imaging is strongly recommended in all patients with HPT. (c) SPET can provide the surgeon with useful information when an EPG is located deep in the neck or mediastinum. (d) IMGP appears to be a useful intraoperative device in HPT patients with solitary parathyroid adenomas and a normal thyroid gland, since it permits minimally invasive and time-saving surgery.     

Importance of radio-guided minimally invasive parathyroidectomy using hand-held gamma probe and low (99m)Tc-MIBI dose. Technical considerations and long-term clinical results.

AIM: (99m)Tc-MIBI radio-guided surgery results, obtained in a group of 141 patients with primary hyperparathyroidism (HPT), are reported. METHODS: All patients were preoperatively evaluated by a single day protocol based on double-tracer parathyroid scintigraphy and neck ultrasound, and then operated by the same surgical team. In 102 patients (72.3%) with a high scan/ultrasound probability of solitary parathyroid adenoma and normal thyroid gland, a minimally invasive radio-guided surgery was planned. In the other 39 patients (27.7%) with scan/ultrasound evidence of multi-glandular disease (n=8) or concomitant nodular goiter (n=31), the intraoperative gamma probe was used during a standard bilateral neck exploration. Intraoperative quick parathyroid hormone (PTH) levels were routinely measured. The minimally invasive radio-guided surgery technique we developed, consisted of: a) injection of a low 37 MBq (99m)Tc-MIBI dose in the operative theatre during anaesthesia induction, b) patient's neck scan with a hand-held gamma probe just before the surgical cut to localize the cutaneous projection of the parathyroid adenoma, c) intraoperative probe detection of the parathyroid adenoma and its removal through a small 2-2.5 cm skin incision. RESULTS: Minimally invasive radio-guided surgery was successfully performed in 99/102 patients (97.0%). The gamma probe was particularly useful in patients with an ectopic parathyroid adenoma in the upper mediastinum (n=11) or to the carotid bifurcation (n=1) or located deep in the neck (n=8). Minimally invasive radio-guided surgery was also obtained in 18/23 patients who had previously undergone thyroid/parathyroid surgery. The mean operative time for minimally invasive radio-guided surgery was 38 min. No major surgical complication was recorded. Conversion to bilateral neck exploration was required in only 3 cases because of intra-operative diagnosis of parathyroid carcinoma (n=2), and persistence of elevated quick PTH levels after removal of the preoperatively visualized parathyroid adenoma (n=1). Among patients treated by standard bilateral neck exploration, the gamma probe was useful in localizing a thymical enlarged parathyroid gland in 1 patient with multi-glandular disease, a parathyroid adenoma located deep in the neck in 4 patients with concomitant nodular goiter and an ectopic parathyroid adenoma to the carotid bifurcation in another. However, in some other patients with a parathyroid adenoma located near to the thyroid, it was difficult to intraoperatively distinguish the parathyroid adenoma from a MIBI avid thyroid nodule. CONCLUSION: It can be concluded that: (a) in primary HPT patients with high scan/ultrasound probability of solitary parathyroid adenoma and normal thyroid gland, the gamma probe appears to be an effective, rapid and safe technique to perform minimally invasive radio-guided surgery; b) a (99m)Tc-MIBI dose as low as 37 MBq appears to be adequate to successfully perform radio-guided surgery; c) the measurement of quick PTH is recommended during minimally invasive radio-guided surgery; d) minimally invasive radio-guided surgery can be performed also in HPT patients with previous parathyroid/thyroid surgery thus limiting surgical trauma; e) with the possible exception of parathyroid adenoma located in ectopic sites or deep in the neck, the gamma probe technique does not seem recommendable in HPT patients with concomitant nodular goiter.     

Parathyroid imaging with pertechnetate plus perchlorate/MIBI subtraction scintigraphy: a fast and effective technique

We set up a modified technetium-99m (Tc-99m) pertechnetate/Tc-99m MIBI (Tc-MIBI) subtraction scintigraphy for parathyroid imaging by introducing the use of potassium perchlorate (KCLO4). Initially, the effect of KCLO4 on technetium thyroid wash-out was evaluated in five healthy volunteers: 40-minute dynamic studies of the thyroid were obtained 20 minutes after the injection of technetium 150 MBq (4 mCi), both in baseline conditions and after the oral administration of 400 mg KCLO4. After an average latency time of 10.5 minutes, KCLO4 administration resulted in fast and relevant technetium thyroid wash-out with a mean half-time of 16.2 minutes (the half-time was 142.8 minutes in baseline conditions), and a 40-minute reduction of thyroid activity of 78% (it was 14% in baseline conditions). Based on these findings, a new Tc-MIBI subtraction procedure was established as follows: 1) 150 MBq technetium (4 mCi) injection; 2) 400 mg KCLO4 administered orally; 3) patient neck immobilization; 4) acquisition of a 5-minute technetium thyroid scan; 5) 500 MBq MIBI (13.5 mCi) injection; 6) acquisition of a sequence of seven MIBI images, each lasting 5 minutes; and 7) processing (image realignment when necessary, background subtraction, normalization of MIBI images to the maximum pixel count of the technetium image, and subtraction of the technetium image from the MIBI images). In addition, high-resolution neck ultrasound (US) was performed in all cases on the same day as the scintigraphic evaluation. Eighteen consecutive patients with primary hyperparathyroidism were enrolled in the study. Tc-MIBI scintigraphy revealed a single adenoma in all cases and US showed this finding in 15 of 18 cases (83.3%). Furthermore, in three patients, a thyroid nodule associated with hyperparathyroidism was detected by technetium thyroid scans and neck US. In all patients, the parathyroid adenoma was easily identified on both the 20- to 40-minute MIBI and subtracted (MIBI-Tc) images. Regarding the scintigraphic parameters, no difference was found between parathyroid adenomas located in the region of the thyroid bed or in ectopic sites and in parathyroid adenomas with a retrothyroid location. Surgical findings confirmed the presence of a single parathyroid adenoma in all cases. In the three patients with a concomitant thyroid nodule, thyroid lobectomy was performed. These preliminary data suggest that 1) double-tracer subtraction scintigraphy, combined with neck US, appears to be the preferable preoperative imaging procedure in hyperparathyroidism patients with concomitant thyroid nodular disease, 2) in the Tc-MIBI parathyroid scan, the use of KCLO4 results in a rapid and relevant technetium thyroid clearance, improving the quality of MIBI images and making the visualization of parathyroid adenomas, particularly those located behind the thyroid gland, easier.     

The usefulness of radio-guided surgery in secondary hyperparathyroidism

Recent reports have shown that radio-guided surgery with an intraoperative gamma probe (IGP) is useful for identifying parathyroid adenomas. The aim of this study was to evaluate the usefulness of IGP mapping in patients with secondary hyperparathyroidism. Seven patients with secondary hyperparathyroidism underwent technetium-99m methoxyisobutylisonitrile (Tc-99m MIBI) scintigraphy immediately before undergoing surgical resection of all parathyroid tissues. We compared the sensitivity of Tc-99m MIBI scintigraphy alone with that of the combination of Tc-99m MIBI scintigraphy and IGP mapping. The sensitivity of the combination of Tc-99m MIBI scintigraphy and IGP mapping was 100% (28 of 28 lesions) and was significantly higher than that of Tc-99m MIBI scintigraphy alone (71.4%, 20 of 28 lesions). The combination of the Tc-99m MIBI scintigraphy and IGP mapping has increased sensitivity for identifying parathyroid lesions during parathyroidectomy in patients with secondary hyperparathyroidism.     

The spectrum of positive scan patterns in parathyroid scintigraphy

Parathyroid scintigraphy provides the clinician treating primary hyperparathyroidism with valuable information regarding the presence and location of parathyroid adenomas. In dual-phase imaging of the parathyroid glands, a widely employed technique that exploits the radiotracer washout characteristics of parathyroid adenomas, images are typically obtained at 20 minutes after administration of the radiotracer (Tc-99m sestamibi or Tc-99m tetrofosmin) and again at 2 hours after injection. Additional imaging of the thyroid is frequently performed to localize thyroid tissue, using Tc-99m pertechnetate or iodine-123.A positive examination can display one of several different patterns; a focus of increased radiotracer activity representing a parathyroid adenoma may be detected on the initial images, on the delayed images, or both. On the thyroid scan, the parathyroid adenoma (if it is discernible) may appear as a cold defect or a persistently hot focus. In our retrospective review of 148 consecutive patients over a 2-year period, 74 examinations were positive and had pathologic confirmation. These examinations were divided into 4 patterns: I (hot focus seen on initial and delayed images, and not on thyroid scan), II (hot focus seen only in initial images), III (hot focus seen only on delayed images), and IV (hot focus seen on initial, delayed and thyroid scan images). Results were as follows: pattern I, 88% (65/74); pattern II, 7% (5/74); pattern III, 3% (2/74); and pattern IV, 3% (2/74).Parathyroid adenomas produce several different patterns on dual-phase scintigraphy. To interpret the examination correctly, it is important for the radiologist to be aware of these patterns of positivity.