Parathyroid Venous Sampling


Primary hyperparathyroidism (PHPT) is an endocrine disorder characterized by autonomic overproduction of intact parathyroid hormone. It is often asymptomatic and identified through routine biochemical screening demonstrating hypercalcemia with elevated or upper normal levels of circulating intact parathyroid hormone. Osteoporosis may occur, and if PHPT remains untreated there is an increased incidence of cancer of the breast, colon, kidney, or prostate. Benign, usually solitary, parathyroid adenomas account for most causes of PHPT. Surgical removal of the hypersecreting gland or glands is considered the treatment of choice. Traditional open, bilateral neck exploration with parathyroidectomy carries a success rate of 95% but comes with a substantial morbidity. Preoperative localization and minimally invasive parathyroidectomy have proved to be as effective and carry a favorable morbidity when compared to open, bilateral neck exploration.

Before surgery, parathyroid adenomas and/or enlarged parathyroid glands can be localized with ultrasonography, multislice contrast-enhanced computed tomography (CT), magnetic resonance imaging, technetium-99m sestamibi nuclear scan, single-photon emission CT, or a combination of sestamibi with single-photon emission CT.

Sugg et al. demonstrated that 5%–10% of patients who undergo surgery will have either persistent or recurrence of PHPT. Common causes for recurrence are unsuccessful preoperative identification of the hypersecreting gland, missed adenoma in multiple parathyroid adenomas, or adenomas in ectopic or undescended parathyroid glands. Reexploration surgery is complicated by scarring and distortion of the tissue planes. Therefore preoperative localization of the site of excess parathyroid hormone secretion is of the upmost importance. If localization with noninvasive imaging is nondiagnostic then parathyroid venous sampling (PVS) is warranted.

Preprocedure

Understanding the embryology of the parathyroid glands allows for precise localization of the hypersecreting parathyroid adenoma with both noninvasive diagnostic test as well as PVS. The inferior parathyroid glands arise from the third branchial cleft along with the thymus, and during development descend with the thymus. This explains why they may be found anywhere from the pericardial sac to the cricoid region. In the mediastinum, they are usually positioned anteriorly. The superior parathyroid glands, which arise from the fourth branchial cleft, are usually more consistent in position posterolateral to the superior pole of the thyroid gland close to the recurrent laryngeal nerve. When ectopic they tend to lie in the superior compartment of the posterior mediastinum.

Knowledge of the parathyroid venous drainage anatomy will increase the success rate of PVS. The parathyroid glands drain via parathyroid veins into the thyroid plexus ( Fig. 77.1 ). Usually there are three paired thyroid veins that form the thyroid plexus: superior, middle, and inferior thyroid veins. The superior and middle thyroid veins drain into the ipsilateral internal jugular vein, whereas the draining pattern of the inferior thyroid veins is more variable. Commonly they drain into the left brachiocephalic vein, either separately or via a common trunk. Alternatively, the common trunk or right inferior thyroid vein drains into the right brachiocephalic vein. Ectopic neck and mediastinal parathyroid glands can drain via various collateral pathways, especially in postsurgical patients. These include but are not limited to the vertebral, thymic, azygos/hemiazygos, and internal mammary veins.

Procedure

After completing the appropriate preprocedural checklists and time-out the right common femoral vein is accessed, most often using ultrasound guidance. A baseline venous sample is obtained from the iliac vein after introduction of the sheath. Once the right atrium has been navigated a long sheath or guide catheter (e.g. 7F, 80 cm long) can be introduced to prevent repetitive negotiation through the right atrium as well as prolapse of the sampling catheter into the right atrium and ventricle. Several shaped 4F or 5 F end-hole catheters are used during PVS. Usually a length of 100 cm is required to reach the target veins in the neck. Commonly used shapes are multipurpose, Cobra, Headhunter, Berenstein, and/or Simmons 2 (see Taslakian et al. for a complete overview). Standard 150-cm hydrophilic angled tip glidewires (Glidewires, Terumo Medical Corporation, NJ) are usually sufficient to negotiate the veins.

Samples from the innominate and internal jugular veins are included; however, sampling the major veins alone is insufficient because the right inferior thyroid vein may drain to the left innominate vein, and mediastinal adenomas may drain to cervical veins and vice versa. The best single vein to start the procedure from is the inferior thyroid vein, especially if there is a single inferior thyroid trunk. Samples should be obtained from both inferior thyroid veins because they are the normal drainage route for both the inferior and superior parathyroid glands. The middle thyroid veins are usually ligated at the first operation. The anterior jugular veins hardly ever drain parathyroid adenomas and should be avoided. The middle thyroid, superior thyroid, vertebral, thymic, and internal mammary veins on each side should be sampled if possible.

Preventing collapse of the venous wall during aspiration through an end-hole catheter can be overcome by adding a small hole to the catheter just proximal to its tip. Alternatively, a 0.018-inch guidewire may be inserted through a Tuohy Borst adapter to prevent the catheter tip from obstructing on the vein wall when a sample is obtained from small veins. Microcatheters can be helpful if these tricks fail and one wants to select smaller veins (e.g., the thyroid venous plexus or the thymic vein). All sampled sites should be marked on a printed diagram and a copy of the diagram sent with the blood samples to ensure correct localization ( Fig. 77.1 )

Fig. 77.1, A diagram such as this one may be copied and used as a standard form when taking parathyroid venous blood samples. One can mark the site of each blood sample and send the marked form along with the blood samples to the laboratory to ensure correct localization.

Care should be taken that the venous samples are processed according to local laboratory standards, which often include immediate cooling and transportation in ice. A 2–3-mL sample volume per sampling location is usually sufficient.

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