72pp issue.indd

B. DIJKSTRA, C. HEALY, L.M. KELLY, E.W. MCDERMOTT, A.D.K. HILL and N.O’HIGGINS

Department of Surgery, St Vincent’s University Hospital, Elm Park, Dublin 4, Ireland

Methods of Pre-Operative Parathyroid Localisation

Intra-Operative Parathyroid Localisation

In patients with primary hyperparathyroidism, neck exploration by an experienced parathyroid surgeon is curative in excess of 95% of cases. Considerable efforts have been devoted to improving parathyroid imaging. New radionucleotide agents and scanning procedures have markedly improved the success rate of localization studies with subsequent development of minimally invasive surgical techniques. In this article we review the different localization techniques and their current role in parathyroid surgery for primary hyperparathyroidism

INTRODUCTION

Parathyroid localisation has evolved through a variety of modalities including non-invasive methods such as ultrasonography (US), computed tomography (CT), magnetic resonance imaging (MRI), and radionucleotide scanning. Invasive methods include angiography, venous sampling, and image-guided biopsy. In 1990, the National Institute of Health (NIH) concluded that pre-operative localisation of the parathyroid glands was unnecessary before initial neck exploration.¹ Bilateral neck exploration performed by an experienced parathyroid surgeon is curative in excess of 95% of cases.² However, the debate of unilateral versus bilateral neck exploration has once again opened the discussion of pre-operative localisation studies, especially with the advances in radionucleotide scanning, notably 99m Technetium radio-labelled Sestamibi, with a reported sensitivity of greater than 90%.³ Localisation with such reliability has generated the potential for minimally invasive parathyroidectomy facilitated by either intra-operative nuclear mapping and/or intra-operative parathyroid hormone (PTH) measurement in initial neck exploration and, also, in re-exploration.^4,5 In this article we review the current status of parathyroid localisation studies in clinical practice.

METHODS OF PRE-OPERATIVE PARATHYROID LOCALISATION

Ultrasound is non-invasive and inexpensive, but is, however, highly operator-dependent. Accuracy with ultrasound is a function of size and location of the adenoma, with poor sensitivity for substernal, retrotracheal and retrooesophageal glands due to acoustic shadowing from overlying bone or air. ^6,7 With a high resolution 10 MHz transducer, nodules of 5mm or more can be detected. Ultrasound is most useful at detecting adenomas around the lower pole of the thyroid, but this area is easily accessible to the surgeon.⁸ Parathyroid tumours posterior in the neck may be localised using a 5MHz-7.5MHz transducer; at these frequencies a deeper penetrance is acquired than using the high resolution 10MHz transducer but at the expense of resolution. False positive interpretation may be due to thyroid nodules, hyperplastic lymph nodes, longus colli muscle or sympathetic ganglia.⁹ The sensitivities of ultrasound in detecting parathyroid adenomas is reported to be between 71-80%.7,10 In one study where 200 patients underwent-unilateral neck exploration the sensitivity was 92.5%.¹¹ However, these patients were selected on the basis that ultrasound showed a localized characteristic solitary adenoma; there was no history of thyroid disease and no family history of hyperparathyroidism or multiple endocrine neoplasia.

Ultrasound is often used in combination with other localisation techniques. Overall, it would appear that ultrasound as a means of pre-operative localisation for unilateral neck exploration is possible but requires considerable technical expertise, the main disadvantage being that it is so highly operator dependent.

Endoscopic ultrasound has been used to localize parathyroid glands, and can be particularly useful for posterior or deep cervical parathyroid glands. Sensitivity has been reported to be 71%, and shown to be superior to standard ultrasonography.¹² (Table 1)

Early studies yielded low sensitivities and specificities with CT for abnormal parathyroid glands, especially in the cervical region, and its use was restricted to the mediastinum particularly for localisation before re-operative surgery.^13,14 However, with more advanced and faster scanners the images have improved considerably. Accuracy depends primarily on the size of the adenoma. The retrotracheal, retroesophageal and mediastinal areas are imaged well, in contrast with ultrasound, but it remains difficult to accurately localize parathyroid glands in the shoulder region and close to or within the thyroid gland.^8,15,16 Differentiating between upper and lower parathyroid glands also is not accurate.^11,17 Adenomas and hyperplastic parathyroid glands are hypervascular and, therefore, an intravenous bolus of contrast is administered to improve the sensitivity of CT to 70-80%. ^18,19 The reported sensitivities range from 46-80%, approaching 80% pre-initial operation, and 46-58% for re-operation.^6,7,17,20 Metallic clips from previous neck surgery create a ‘sparkler’ effect and distort the image.¹⁶

Computed tomography on its own is limited but CT in combination with other modalities has a place in localisation, especially for re-operation for hyperparathyroidism. It can also be used in combination with fine needle aspiration for measurement of PTH, and cytology.²¹ (Table 1)

Table 1: Range of sensitivities and specificities for various localisation modalities

Magnetic resonance imaging, also a cross-sectional imaging modality, offers excellent soft-tissue definition without the need for intravenous contrast material. It can be used to examine the neck and thorax in transverse, sagittal and coronal planes of section. Normal parathyroid glands are smaller than 5mm and cannot be seen because of limited spatial resolution.²² Magnetic resonance imaging produces T1- and T2-weighted images; enlarged parathyroid glands display a medium intensity on T1-images, like thyroid or muscle, but have considerable increased intensity on T2- and proton density images.^22-25 Parathyroid adenoma cannot be discriminated from hyperplasia or carcinoma by image intensity, or by T1 or T2 measurements.^16,22

Figure 1b: At 2 hours (b) demonstrating the presence of a large
solitary parathyroid adenoma in the lower pole of the right thyroid lobe

Figure 1c: Ultrasound transverse view confirms
the presence of a solid nodule in this region (arrow). This enabled
a minimally invasive unilateral excision of the adenoma to be performed

High resolution MRI with local (surface) coils have been reported to have a sensitivity of 74% and specificity of 88%,²⁴ but problems arise with ghost artefacts from respiratory-movement as the coil sits directly on the neck and thorax. This difficulty can be reduced by stabilizing the coil in a rigid holder.

Because MRI images the neck and thorax, it is useful in localizing ectopic parathyroid glands, with up to 88% sensitivity reported.^16,18,26 The majority of ectopic glands are in the thymus-or para-oesophageal areas of the mediastinum.

Gadolinium injected intravenously can substantially enhance the signal intensity of the abnormal parathyroid glands and improve the differential contrast with neighbouring tissue on T1-weighted images, but does not improve contrast with the surrounding tissue beyond that which can be achieved on T2-weighted images. Thus, it has not improved lesion detection beyond that obtained from the combination of T1- and T2- weighted images.²⁷ Short tau wave inversion recovery (STIR) has improved the images further; STIR serves to suppress the signal from fat and highlight the signal from areas of high tissue-water content. These images are relatively poor in anatomical resolution but the lesion is detected more easily as it is enhanced with the suppression of fat. The STIR images are then compared with the more anatomically superior T1-weighted images in two planes to allow precise localisation of the lesion. The use of STIR has resulted in a sensitivity of 71% and a specificity of 94%.²⁸ Magnetic resonance imaging can clearly distinguish scar tissue from parathyroid tissue and, therefore, is particularly useful in the re-operative setting, with 50-88% sensitivity.^16,18,22

Thallium-technetium subtraction scanning relies on the differential uptake of these isotopes by the thyroid and parathyroid glands. Thallium chloride is taken up by both thyroid and parathyroid, particularly hyperfunctioning glands, and technetium 99m pertechnetate is concentrated only by the thyroid. Using computerized digital subtraction of the scans, one can detect the image of a parathyroid tumour. Accuracy is dependent on size, spatial resolution being about 5mm, and location with lesions closest to the surface more readily detected. Sensitivity is reported at 75% at initial investigation and 50% in re-operative cases.^7,8,16,18,31 False positive results occur with metastatic nodal disease, as well as benign and malignant thyroid tumours, and false positive rates of up to 25% have been reported, especially in re-operative patients.^{7,16,18,29,30} These findings and the lack of anatomic detail demonstrated by this method have rendered it as a second-line imaging modality and, thus, unsuitable for routine pre-operative localisation. (Table 1)

Overall, MRI sensitivity ranges from 64 to 78% and specificity from 88 to 95%.^6,7,24,28 However, it remains an expensive imaging modality, there are problems in some patients with claustrophobia, and it cannot be used easily in guiding needle aspiration. Its use is not justified in routine pre-operative localisation. (Table 1)

Sestamibi is a lipophilic, cationic, isonitrile derivative of technetium. It was incidentally observed that sestamibi, used for myocardial perfusion imaging, was taken up and retained in abnormal parathyroid tissue.³² The actual mechanism of uptake remains unclear. Mitochondria and P-glycoprotein, a membrane transport protein encoded for by the multidrug resistence gene, have both been implicated.^33,34 The large number of mitochondria present in cells of parathyroid adenoma may be responsible for the high uptake and slow washout seen in parathyroid adenoma, compared with the surrounding thyroid tissue.

The favourable physical characteristics of sestamibi include high-energy photon emission and a short half-life, permitting high definition three-dimensional imaging and limiting the radiation dosage delivered to patients. Thus, sestamibi imaging provides the opportunity for functional identification of parathyroid tissue in combination with three dimensional anatomic detail when single photon emission computed tomography (SPECT) is used.^35-38

There are currently three technical methods for pre-operative localisation with sestamibi; single isotope dual-phase scan dual isotope subtraction scan, and three dimensional SPECT imaging. Single isotope dual-phase scanning is the simplest procedure. It was first described by Taillefer et al in 1992.39 Cervico-thoracic planar imaging is performed at 15 minutes and then 2-3 hours after intravenous injection of 15-25 mCi 99m Tc-labelled sestamibi (approximately 740mBq). A positive scan for parathyroid disease is defined as an area of increased uptake which persists on late imaging.³⁹ Dual isotope-subtraction scanning combines 99m TC sestamibi with another radioisotope which is specific for the thyroid gland, the images are then subtracted to allow detection of focal uptake within the abnormal parathyroid tissue. Several technical variants have been described, including thallium chloride and iodine 123.40,41 Controversies exist regarding the amount of radiotracers injected, the order in which they are injected, and the subtraction technique.^39,42 Single isotope dual-phase scanning eliminates these technical debates.

Three dimensional studies using SPECT allows better localisation anatomically. However, only a marginal improvement in the overall detection rate is reported.^42,43 In addition, the added cost does not justify routine use of this technique, but it may be useful in the re-operative, difficult localisation. Anterior planar views, in combination with lateral or oblique views, of the parathyroid glands are usually sufficient to ensure adequate localisation.

Currently, there are considerable data available to support the use of sestamibi scanning as a pre-operative localisation technique for unilateral neck exploration and minimally invasive parathyroidectomy.^3,44-46

A multicentre prospective study using single isotope dualphase scanning by Caixas et al (1997) reported a sensitivity of 97% and specificity of 100% (n=70).⁴⁷ The control group in this study (n=20) showed that no single normal gland had a positive scan. O’Doherty et al (1992) used subtraction scanning with administration of oral 123 iodine, four hours before anterior planar imaging, and reported a sensitivity of 97.5% and specificity of 100% (n=39).³³ Malhotra et al (1996) combined all three technical variants of sestamibi in their prospective study of 26 patients.⁴⁸ They began with single isotope dual-phase scanning, then used subtraction scanning and also used SPECT imaging to precisely pinpoint ectopic glands. Sensitivity was reported at to be 100%. This study demonstrates the versatility of sestamibi scanning and how using subtraction or SPECT overcomes potential difficulties with single isotope scanning. A meta-analysis of the English literature over ten years to determine the collective sensitivity and specificity of sestamibi scanning was published in 1998, the average sensitivity being 90.7% and specificity 98.8% (n=784).³ (Table 1)

A positron emitting analogue of D-glucose, 2-(fluorine-18-fluoro-2-deoxy-D-glucose (FDG), allows glucose metabolism to be measured and evaluated using PET. Aerobic glycolysis is prevalent in many neoplastic tissues, and the rate of glucose metabolism tends to be much higher than in normal tissues. The patient is given up to 10 mCi (370 MBq) of FDG intravenously and regional body emission scans are obtained in different planes and recorded digitally for analysis.⁴⁹ There is differential concentration of FDG in abnormal parathyroid tissue and this difference is used to localize the abnormal gland(s). However, FDG also accumulates in other malignant and benign tissues, and in inflamed or infected tissue. This may potentially limit the use of PET scanning as FDG may also be taken up by thyroid tissue in thyroiditis or in thyroid adenoma, carcinoma, as well as other malignant tissues in the neck or superior mediastinum.. Accuracy of PET for localisation has been reported to range from 85 to 94% for adenomas, and 50% for hyperplasia.⁴⁹ When compared with sestamibi scanning, PET was found to be more sensitive, although in this study the sensitivity for sestamibi was considerably less than reported elsewhere.^3,50 It has also been studied in localisation for recurrent or persistent hyperparathyroidism and found to be accurate in up to 79% of adenomas and 29% of hyperplasias,⁵¹ It may be a useful technique in this setting, especially when sestamibi scanning has failed to localize the abnormal gland(s).⁵² PET has also been studied with the use of L-(carbon-11)-methionine instead of FDG with similar results (80-85% accuracy).^53,54

However, promising, PET scanning as a localisation technique remains experimental and further studies are awaited. It is also expensive and, therefore, limited in its use as a regular preoperative investigation. Its role as a localisation tool may be in difficult cases prior to re-exploration. (Table 1)

These two investigations have a combined sensitivity of 91-95%, with a low incidence of false positive examinations.7 Detailed anatomic localisation is possible. However, because it is expensive, invasive and has the potential complications of contrast toxicity, embolization and neurological damage, and is very time-consuming, it is usually reserved for patients with previously unsuccessful neck explorations.

Arteriography involves highly-selective injections of contrast into the inferior and superior thyroid arteries or internal mammary arteries and is combined with digital subtraction. All enlarged parathyroid glands are highly vascular and these are readily identified by a persistent angiographic ‘stain’, glands of 4mm or more can be identified.^7,55 Granulation tissue can sometimes be hypervascular but is distinguishable by a blurred or absent margin. Lymph nodes and muscle are hypovascular. Equivocal findings occur in 10-15% of cases and are related to thyroid nodules or intrathyroid parathyroid adenomas.⁷ Ectopic tumours can be demonstrated by this technique.^7,55 Granulation tissue can sometimes be hypervascular but is distinguishable by a blurred or absent margin. Lymph nodes and muscle are hypovascular. Equivocal findings occur in 10-15% of cases and are related to thyroid nodules or intrathyroid parathyroid adenomas.⁷ Ectopic tumours can be demonstrated by this technique.

Arteriography can be performed with consideration of possible transcatheter tumour ablation, by injecting high-osmolar ionic contrast which causes ischaemia and necrosis of the abnormal parathyroid gland. In a NIH series of 24 patients, 70% of patients were free of their hypercalcaemia after 5 years.⁵⁶

Arteriography is often combined with venous sampling. Sampling after angiography rarely produces false positive results,⁵⁷ but sampling without prior angiography has a false positive rate of 6-18%.⁵⁸ Extensive sampling of the thyroid venous plexus and thymic veins is necessary. As it is a functional study, differentiation between hyperplasia and adenomas is possible. Adenomas produce unilateral or focal hypersecretion of PTH whereas hyperplasia demonstrates elevated PTH throughout the venous plexus bilaterally.7 A two-fold gradient between PTH in the sampled vein and a peripheral vein is required for confident localisation. Sensitivities of 70 to 80% have been reported.^11,16,55 (Table 1)

INTRA-OPERATIVE PARATHYROID LOCALISATION

An experienced surgeon performing a bilateral neck exploration for primary hyperparathyroidism should have a cure rate in excess of 95%.² The rationale for bilateral neck exploration is that a subset of patients have multiglandular disease due to hyperplasia or multiple adenomas, which could potentially be missed if all four glands are not visualized.⁵⁹

However, in a recent meta-analysis based on 6,331 patients, the incidence of a single adenoma was 87%, four-gland hyperplasia 9%, multiple adenoma 3%, and cancer less than 1%.³ Therefore, if one excludes patients with familial hyperparathyroidism and Multiple Endocrine Neoplasia (MEN) syndromes, a single adenoma should be encountered in more than 90% of cases.

Moreover, it has been shown that not all patients have all four glands visualized during bilateral exploration. In one institution, 44% of cases had all four glands visualised and in 37% three glands only were identified.⁶⁰

With the sensitivity and specificity of sestamibi scanning now in the order of 91% and 98.8%, respectively,3 a less invasive more directed approach could have similar success rates with potentially shorter operating time, improved cosmesis and reduced morbidity.

Figure 2b: At 2 hours (b) reveals an ectopic parathyroid adenoma
at the level of the thoracic inlet just to the left of the midline.

Figure 2c: CT scan, post-intravenous injection of contrast confirms the presence of
a nodule at this site (arrow). The adenoma was found in the upper part of the left thymus at exploration

Prior to accurate pre-operative localisation, unilateral exploration was performed by some groups.^61,62 The decision as to which side to explore was entirely random, and if no adenoma was found then a bilateral exploration was performed. Unilateral exploration was possible in 34-42% patients, when the adenoma was excised and one normal gland was seen on that side. The operative time for those in whom unilateral exploration was possible was significantly shorter.⁶²

Currently, with the use of pre-operative sestamibi scanning providing accurate localisation of the adenoma, unilateral exploration is becoming more successful. Several series have reported 95-100% surgical success and operative times in the order of 40-50 minutes, with minimal complications.^3,63-66 Patients suitable for unilateral exploration need to be selected, and those with MEN syndrome, familial hyperparathyroidism, and suspected hyperplasia or multiple adenomas are not suitable candidates for unilateral exploration.

This technique is increasingly being used to ensure successful excision of all the abnormal parathyroid tissue at the time of surgery. The rapid PTH assay, with a turn-around time of 10-15 minutes, is a modification of the standard assay ( which takes 2 hours) and has an excellent correlation with it. It is a realtime quantitative assay using the immunochemilluminescence method, as compared with the standard assay which uses the immunoradiometric method. Prior to skin incision a baseline venous blood sample is taken from a peripheral vein. Further samples are taken five and ten minutes after removal of the abnormal parathyroid gland. Within 10-15 minutes the results are available. A drop in PTH level greater than 50% from the highest pre-excision level to that ten minutes after excision of the adenoma meets the criterion for successful removal of the abnormal parathyroid gland67. As the half-life of intact PTH is 3-4, minutes 88% of patients will meet the criterion within 5 minutes and 95% within 10 minutes.⁶⁷

Use of this intra-operative rapid PTH assay has improved success rates at initial parathyroidectomy from 93 to 98% in some series.^68-70

In re-operative parathyroid surgery rapid PTH assay can be used as a localisation tool as well as to confirm that all hyperfunctioning tissue is excised. This assay has led to an improvement in re-operative success rates from 76% to 94%.⁷¹

The true advantage of this technique is the certain knowledge during the operation that the hyperparathyroid state is corrected. It can be utilized, therefore, in more directed, minimally invasive parathyroidectomy procedures, where it is not always possible to see an ipsilateral normal parathyroid gland.

This technique involves pre-operative localisation using a dual-phase sestamibi scan with anteroposterior and left and right oblique views of the neck. Only those patients with a definite solitary parathyroid adenoma are suitable for this approach.

Surgery is performed within 1.5 to 3 hours post-injection of sestamibi, so that the abnormal parathyroid gland is still radioactive. A hand-held gamma probe is used intraoperatively to guide the surgeon to the adenoma. All four quadrants of the neck are checked for radioactivity using the probe and there should be a difference of approximately 500 counts per second overlying the adenoma, compared with the rest of the neck. Once the adenoma is excised, the gamma counts decrease with establishment of the new background level of radioactivity which equalizes in all four quadrants of the neck. The excised adenoma should emit gamma counts greater than 20% post-excision background counts.4 The use of the gamma probe helps to eliminate the possibility of inaccurate or false-positive scans, and the requirement of equilibration of all four quadrants prior to ceasing exploration is used to avoid leaving further hyperfunctioning glands behind. The advantage of this procedure is improved cosmesis. A smaller incision can be made as the use of the gamma probe allows the surgeon to be very directional. This also allows the procedure to be performed under local anaesthesia. The operating time is considerably shorter, and the patient can be discharged home earlier.^4,72,73

However, the procedure does require an experienced nuclear medicine physician, and a close working relationship is essential. The timing of images is critical as there is a short operative window from 1.5 to 3 hours post-injection of the sestamibi.⁴

A limited dissection does pose potential risk to the recurrent laryngeal nerve, as this is not always accurately identified. If the procedure is performed under local anaesthesia, there is an increased risk of the nerve entering the operative field if the patient swallows during the procedure.

Radiation exposure is reported to be safe, the cumulative radiation dose acquired with fifteen cases being only 1% of acceptable yearly exposure (5 rem).⁴

Intra-operative PTH assays can also be used with this minimally invasive technique to ensure adequate resection of all abnormal glands.⁷² The use of the gamma probe has been very useful in the patient with persistent or recurrent hyperparathyroidism requiring re-exploration, the only difference being that the sestamibi scan is obtained prior to surgery, and the patient is re-administered the isotope on the day of surgery with the exploration being performed within 3 hours of injection of the sestamibi.⁵

Parathyroid exploration under local anaesthesia was initially described in patients who were thought to be at high risk for general anaesthesia. Pre-operative localisation is mandatory and, in the era before sestamibi scanning, there was a significant failure rate (20%).⁷⁴

The use of local anaesthesia is now well described in association with minimally invasive techniques, either unilateral directed exploration^20,75,76 or in association with radioguided parathyroidectomy.^4,5,72,73,77 Benefits include reduced requirementsof post-operative analgesia, shorter inpatient time and subsequent cost savings.

Although this is technically feasible there are concerns regarding complications, such as recurrent laryngeal nerve palsy, rupture of the adenoma during removal through a small incision and persistent hyperparathyroidism.^78,79 The use of intra-operative PTH assay could reduce this latter risk.

The endoscopic procedures range from a pure endoscopic approach with constant gas insufflation to a video-assisted gasless technique. All patients require accurate localisation of a solitary parathyroid adenoma pre-operatively. Exclusion criteria are; previous neck surgery, concomitent goitre, neck radiation, abnormal neck anatomy and suspicion of multigland disease.

Endoscopic parathyroidectomy using carbon dioxide insufflation has been associated with complications such as extensive subcutaneous emphysema (from eyelids to scrotum) which resolved after 3 days without any persistent morbidity80. There may also be problems with hypercapnia and tachycardia. Another disadvantage is the small working space and limited visability, especially, if there is any bleeding. Operating times tend to be longer than for open parathyroidectomy.^80,81 It has been performed through midline neck incisions, as well as away from the neck through the axilla or anterior chest wall with potential for improved cosmesis.

The video-assisted technique only uses carbon dioxide insufflation for three minutes at the start of the procedure to develop a working space under the strap muscles. The space is then maintained by means of skin retractors to allow parathyroidectomy to be performed under telescopic vision through a 1.5cm central neck incision. Intra-operative PTH assay is used to ensure complete removal of all hyperfunctioning tissue.⁸² It has also been described through a lateral neck incision.⁸³ Comparative studies with the open procedure show there is no difference or slight improvement in operative time.^84,85

Complications are similar to the open procedure in the larger series, suggesting there is a learning curve. Care needs to be taken when removing the adenoma through a small incision to prevent rupture and possible development of parathyromatosis.⁸² Benefits include improved cosmesis and less post-operative pain.^82-85

Endoscopic parathyroidectomy with limited gas insufflation appears feasible, but requires training and should be performed by experienced parathyroid surgeons to ensure a 95 to 98% success at the initial operation.⁷⁹ It is difficult to envisage that it will find a role in routine parathyroidectomy.

CONCLUSION

Parathyroid localisation has an important role in patients undergoing unilateral neck exploration or a minimally invasive approach for parathyroidectomy. Of the localisation studies available, sestamibi scanning is the most sensitive and specific. Accurate pre-operative localisation is now possible enabling a more directed unilateral exploration to be performed with similar high success rates to bilateral neck exploration. Patient selection is very important, and accurate pre-operative localisation of a solitary adenoma is mandatory. For the patient with multi-gland disease, familial primary hyperparathyroidism, MEN syndrome, secondary hyperparathyroidism, previous neck surgery or radiotherapy, bilateral neck exploration remains the procedure of choice.

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Correspondence: Professor N. O’Higgins, Department of Surgery, St Vincent’s University Hospital, Elm Park, Dublin 4, Ireland

Study Type	Sensitivity	Specificity
Ultrasound^7,10	71-80%	80%
Endoscopic Ultrasound¹⁰	71%
CT Scan^6,7,17,19	46-80%	88-98%
MRI Scan^6,7,24,28	64-78%	88-95%
Thallium-Technetium Scan^7,8,16,18	75%	73-82%
Technetium-Sestamibi Scan³	90.7%	98.8%
PET Scan^49,51,53,54	80-94%
Angiography & Venous Sampling⁷	91-95%	96-98%
Venous SamplingAlone^11,16,55	70-80%

CLINICAL REVIEW

Parathyroid localisation - current practice

INTRODUCTION

METHODS OF PRE-OPERATIVE PARATHYROID LOCALISATION

INTRA-OPERATIVE PARATHYROID LOCALISATION

CONCLUSION

REFERENCES