2005

Primary Aldosteronism: The Role of Adrenal Venous Sampling

Points to Remember

• Minimally invasive parathyroidectomy may be appropriate for up to two-thirds of patients with primary hyperparathyroidism undergoing initial surgical treatment.
• With minimally invasive parathyroidectomy, an outpatient procedure with local anesthesia is an option.
• Minimally invasive parathyroidectomy is associated with a smaller incision, shorter hospitalization time, and faster postoperative recovery.

Primary hyperparathyroidism (HPT) is the most common cause of hypercalcemia, affecting as many as 1 per 1,000 women over the age of 60 years. Cure of primary HPT reliably benefits patients with osteoporosis or osteopenia and those with subtle but clinically significant neuropsychiatric and muscular symptoms. These benefits may be expected regardless of the level of hypercalcemia, even when the serum calcium level is less than 11.0 mg/dL. Standard bilateral cervical exploration is a safe and effective procedure, with a cure rate higher than 95% and risk of recurrent laryngeal nerve damage or hypoparathyroidism of less than 1%. This high level of success in curing the disease and minimizing complications has led to patient-focused improvements and has prompted a shift from standard open surgical approaches to minimally invasive techniques. Minimally invasive parathyroidectomy (MIP) has emerged as a popular method in endocrine surgery (Figures 1-4). Several key advances have facilitated the development of MIP:

• High-quality parathyroid adenoma localization techniques
• High-quality, rapid intraoperative parathyroid hormone (PTH) measurement
• Small-incision outpatient procedure

Enlarge

High-Quality Localization Techniques

The sensitivity and specificity of high-resolution, real-time small parts ultrasonography are approximately 70% and 90%, respectively, in adenoma localization, provided that highly expert radiologists are performing the examination. It is noninvasive and the most inexpensive preoperative localization technique. It is anatomically precise and capable of identifying 95% of adenomas weighing more than 1,000 mg. However, ultrasonography identifies less than 50% of adenomas weighing less than 200 mg. The key limiting factor for ultrasonographic localization is its extreme dependence on the operator.

The introduction of technetium-sestamibi (MIBI) scanning in 1989 advanced preoperative localization. The 1990 National Institutes of Health Consensus Development Conference on Diagnosis and Management of Asymptomatic Primary Hyperparathyroidism concluded that preoperative localization was not indicated in patients with asymptomatic HPT who had not undergone prior neck exploration. However, throughout the 1990s, preoperative localization was used in at least 75% of patients. With or without thyroid subtraction scan, often with the addition of SPECT imaging and oblique views, MIBI scanning has become the localization procedure of choice. It is minimally invasive and depends on physiologic hyperfunction of the enlarged parathyroid gland rather than pure anatomic identification. Adenomas anywhere in the neck or mediastinum can be localized. MIBI scanning is somewhat less dependent than ultrasonography on the size of the parathyroid adenoma for imaging, but the cost is usually higher. A major advantage of MIBI over ultrasonography is its minimal dependence on operator experience to obtain a high-quality scan. The generally accepted overall sensitivity of MIBI scanning is 75% to 80%.

The Mayo Clinic Experience

In June 1998, we gradually introduced MIP at Mayo Clinic. Through March 2004, we performed 1,534 parathyroid operations. Excluding reoperative parathyroid surgery, the total of 1,365 included 738 conventional procedures (54%), 602 MIPs (44%), and 25 procedures (2%) that were converted from MIP to a conventional approach. The cure rate for both conventional open exploration and MIP was 97%. Localization was performed with MIBI scanning (1,250 patients) and ultrasonography (506 patients). The sensitivity and positive predictive value of MIBI were 86% and 93%, respectively, whereas comparable figures for ultrasonography were 61% and 87%. Important to these figures is the median weight of the largest resected parathyroid gland of 420 mg, and a mean calcium value of 10.9 mg/dL (reference range, 8.9-10.1 mg/dL).

Of the patients undergoing MIP, 339 (56%) received general anesthesia, and 263 (44%) had a combination of local anesthesia and intravenous sedation. Of these, 295 patients (49%) were dismissed from the hospital the day after the operation, whereas 278 (46%) had outpatient procedures. Intraoperative PTH monitoring was used in 682 patients, with sensitivity, positive predictive value, and accuracy rates of 98%, 99%, and 98%, respectively. The true-negative rate, defined as no decline in the PTH value when the patient still had an additional enlarged parathyroid gland, was 8% in this series.

Numerous factors precluded the use of MIP in the patients who underwent conventional surgery: 244 were reoperative cases (parathyroid related, 164; prior thyroidectomy and other neck procedures, 80); 38 were parathyroid related (multiple endocrine neoplasia, familial HPT, etc); 216 had localization problems; 51 had combined operations requiring general anesthesia; and 109 were combined with thyroidectomy.

The successful outcome of parathyroid surgery, specifically MIP, depends on a highly skilled and experienced multidisciplinary team. The endocrinologist, nuclear medicine specialist or ultrasonographer, clinical laboratory and intraoperative PTH technician, and surgeon as well as the nursing and paramedical staff all must function together smoothly and efficiently to achieve consistently successful outcomes. The general accuracy of intraoperative PTH has been widely verified and enthusiastically supported. Local anesthesia, a small incision, and brief outpatient recovery are further advantages of the unilateral MIP approach.