In approximately 75 - 90 % of cases, primary hyperparathyroidism (pHPT) is due to a solitary parathyroid adenoma (PT adenoma). While double adenomas are rather rare, hyperplasias of all four PTs are somewhat more common. The latter are predominantly genetically determined and occur with familial clustering. In < 1 % of cases, a PT carcinoma is present. With a prevalence of 0.2 - 0.4% in those over 60 years of age, pHPT is one of the three most common hormonally induced diseases in the population [1, 2, 3].
Localization Diagnostics of PT Adenomas
While bilateral neck exploration was common until about 20 years ago [4], focused surgical techniques are now in the foreground. Once the biochemical diagnosis of pHPT has been made, localization diagnostics follow.
Ultrasound is the localization diagnostic tool of first choice, with which about 70 % of PT adenomas can be visualized [5]. Similarly good results can be achieved with Tc-99m-Methoxyisobutyl-Isonitrile(MIBI)-Scintigraphy. The informative value of scintigraphy can be further improved by using SPECT technology [6]. SPECT (Single Photon Emission Computed Tomography) combines gamma camera and computed tomography and enables three-dimensional imaging of the compartment to be examined. In contrast to ultrasound, scintigraphy can also visualize mediastinally located adenomas.
The sensitivity of computed and magnetic resonance tomography is reported in the literature as 30 – 80 % and is thus below that of ultrasound and scintigraphy.
With 11C-Methionine-Positron Emission Tomography(PET)-CT, a portion of PT adenomas can be localized that cannot be visualized with other imaging methods [7]. However, the procedure cannot be performed at the expense of statutory health insurance (as of: 2017).
In selective venous blood sampling from the jugular veins, the brachiocephalic vein, and the superior vena cava, the determination of PTH concentration in the blood samples can contribute to narrowing down the adenoma localization if values are elevated. The procedure is not indicated for primary operations.
Focused surgical techniques require ultrasound and, if necessary, scintigraphy; further examinations for adenoma localization must be viewed critically. Before a primary operation, the surgical indication for PT adenoma should not be made dependent on successful localization diagnostics. Exceptions are previous thyroid surgeries due to the increased surgical risk.
Surgical Indication
The surgical indication is given for all patients with classic symptoms and secondary diseases of pHPT. In supposedly asymptomatic patients, the indication is discussed controversially [8, 9]. According to the recommendations, asymptomatic patients should be operated on if
- they are younger than 50 years or
- have a calcium level of more than 0.25mmol/l above the upper normal value or
- a creatinine clearance of less than 60ml/min or
- a calcium excretion in the urine of more than 10mmol/day.
The surgical indication should also be considered if
- the bone density measurement yields a T-score of < - 2.5,
- a vertebral body fracture is present,
- imaging diagnostics show asymptomatic kidney stones or nephrocalcinosis.
In many supposedly asymptomatic patients, an improvement in quality of life is also observed after successful surgery [10]. If no surgery is performed, annual follow-up examinations are recommended (calcium level, bone density measurement, imaging diagnostics of the kidneys).
Focused Surgical Technique
This term encompasses various surgical techniques with which a preoperatively localized PT tumor is specifically sought and removed [11, 12, 13]. Preparation on the contralateral side with corresponding surgical risks and postoperative scarring is thus avoided.
The previously common bilateral neck exploration with visualization of all four PTs is indicated in patients who likely have multigland disease, or if no PT adenoma could be localized preoperatively or there is no possibility to perform intraoperative PTH level measurement.
Intraoperative PTH Determination
To monitor the success of focused surgical techniques, intraoperative PTH determination is required. If no further adenoma is present, the PTH level drops within a few minutes after adenoma removal due to the short half-life of PTH. The procedure can be ended in these cases. If the PTH level does not drop, the contralateral side must be explored. According to the European Society of Endocrine Surgeons, intraoperative PTH determination can be dispensed with if the adenoma was localized preoperatively both with ultrasound and scintigraphy [14].
Various recommendations exist for the interpretation of intraoperatively obtained PTH values [15], which relate to the timing of blood draws and the required PTH drop. In the USA, the “soft” Miami criteria are common (drop in PTH level after adenoma removal to < 50 % of the baseline value), in Germany, however, the “hard” Halle criteria (drop in PTH level < 35 pg/ml). With the Miami criteria, there is a risk of overlooking multigland disease, with the Halle criteria, the risk is greater of unnecessarily exploring the contralateral side.