Nonlocalizing Parathyroidectomy
Keith S. Heller
INTRODUCTION
For many years, the standard operation for primary hyperparathyroidism (HPT) was a bilateral cervical exploration identifying all four parathyroid glands and removing the one(s) that were abnormal. Abnormal parathyroid glands were recognized by their size and substance when palpated directly. Some surgeons routinely biopsied normal and abnormal parathyroid glands to confirm their identity, but most did not. As imaging techniques were developed and improved, particularly 99Tc sestamibi scanning, high-resolution ultrasonography, and computed tomography (CT) scanning, surgeons used them with increasing frequency to help localize the abnormal parathyroid glands but continued to identify all four parathyroid glands at the time of surgery. These imaging studies, either alone or in combination, can accurately predict the location of solitary parathyroid adenomas in most patients but are much less reliable in identifying the 15% of patients who have more than one hyperfunctioning parathyroid gland. Whether or not preoperative imaging was employed, the success rate for this approach was >95%.
More recently, many surgeons have adopted the practice of focused, single-gland exploration. In this approach, preoperative imaging identifies the parathyroid adenoma. Without performing a complete bilateral exploration, the adenoma is identified and removed. Most surgeons confirm the adequacy of the procedure by measuring parathyroid hormone (PTH) levels intraoperatively (IOPTH). A fall in IOPTH of at least 50% from a baseline value and into the normal range is considered sufficient evidence that the remaining parathyroid glands are normal, so the operation can be terminated without identifying the remaining parathyroid glands. This approach results in cure rates comparable to conventional bilateral exploration.
Although focused, single-gland exploration is performed with increasing frequency, there remain situations in which conventional bilateral exploration is required. In some patients, imaging studies fail to identify any abnormal parathyroid glands. This can occur in the presence of a multinodular goiter that makes the preoperative identification of enlarged parathyroid glands difficult. Small, but abnormal, parathyroid glands can be difficult to image particularly in the presence of four-gland hyperplasia where all four parathyroid glands may be only minimally enlarged. In some clinical situations (secondary and tertiary HPT, familial HPT, multiple endocrine neoplasia syndromes) routine bilateral exploration is recommended regardless of the results of preoperative imaging because of the prevalence of four-gland hyperplasia. A standard, systematic surgical approach is required to identify all abnormal parathyroid glands in these situations.
HISTORY
Most patients with HPT are identified by the finding of an elevated serum calcium level on routine blood tests. The presence of elevated PTH levels and elevated calcium levels is virtually always diagnostic for HPT. In about 15% of patients, however, normocalcemic HPT is discovered during the evaluation of a patient with renal calculi, osteoporosis, or subjective symptoms suggestive of HPT. Once the diagnosis is established and the decision made to proceed with surgery, appropriate imaging studies are ordered.
PHYSICAL EXAMINATION
Enlarged parathyroid glands are almost never palpable. A palpable mass in the midline inferior in the neck in a patient with HPT is usually a thyroid nodule that should be evaluated by ultrasonography and fine needle aspiration (FNA) if appropriate. Rarely, very large parathyroid adenomas or carcinomas can be palpated. The latter are extraordinarily rare and are usually associated with very high serum calcium levels. Lethargy, confusion, and frank coma can occur in the presence of severe hypercalcemia, but many patients with serum calcium as high as 12 or 13 mg/dL have no abnormal physical findings or symptoms. The presence of a scar or scars in the inferior aspect of the neck should alert the examiner to possible previous thyroid or parathyroid surgery. Tracheal deviation is suggestive of a substernal goiter. These findings can make parathyroid exploration more difficult. In addition, a patient with a short, thick neck, frequently associated with the cricoid cartilage at the level of the sternal notch, can be very challenging technically.
INDICATIONS
The number of patients referred for parathyroid surgery continues to increase. Reasons for this trend include the recognition that significant HPT can exist in the presence of normocalcemia (15% of patients undergoing surgery), a greater awareness of the relationship of osteoporosis to chemically mild HPT, and better patient acceptance of parathyroid surgery particularly when focused, single-gland exploration is performed. This operation is frequently done under local anesthesia without overnight hospitalization with minimal postoperative discomfort or disability. Objective indications for parathyroid surgery include the following:
Serum calcium >1 mg/dL above normal
Renal calculi
Osteoporosis
Age <50 years
Creatinine clearance <60 mL/minute
Other factors that can be considered in deciding whether or not surgery should be performed include subjective neurocognitive symptoms, bone pain, and fatigue as well as patient preference. The absence of any of the indications listed above is not a contraindication to surgery. Many endocrinologists and surgeons recommend parathyroid surgery for totally asymptomatic patients. Of course, prior to recommending surgery, the diagnosis of primary HPT must be confirmed. In general, imaging studies are used to help in the planning of surgery but are not required to establish the diagnosis of HPT.
CONTRAINDICATIONS
There are virtually no contraindications to parathyroid surgery other than severe coexisting medical conditions. It might be reasonable, however, to avoid difficult reoperative surgery with a higher risk of complications and a lower success rate in a patient in whom observation is a reasonable alternative to surgery.
PREOPERATIVE PLANNING
Imaging
Most patients in whom parathyroidectomy is planned undergo preoperative imaging studies. It is not the intent of this chapter to go into a detailed discussion of the different imaging studies available. Each has its advantages and disadvantages. Ultrasonography is inexpensive and risk free. It can also be performed at the time of initial consultation by the operating surgeon. Ultrasonography is not useful in identifying adenomas that are retrosternal or located deep in the neck (behind the trachea or esophagus). 99Tc sestamibi radionuclide scans (usually performed as single photon emission computed tomography scans sometimes with CT image fusion) can detect adenomas in ectopic locations. CT scanning with contrast is gaining increasing popularity. It is important to remember that the accuracy of each of these techniques is very dependent on the experience of the radiologist interpreting the study. There is also considerable difference of opinion as to whether one imaging study or multiple imaging studies should be performed. Most surgeons use a single study or a combination of ultrasonography with one of the other studies. If the two studies are negative or discordant, it is reasonable to perform a third study in selected cases particularly if a focused, single-gland exploration is planned. A magnetic resonance imaging scan is unlikely to add further information to the other three studies. Angiography and selective venous sampling are not recommended as part of the evaluation of patients who
have not had previous, parathyroid surgery. If imaging is negative or discordant or if imaging suggests more than one abnormal parathyroid gland, then a conventional bilateral exploration is planned.
have not had previous, parathyroid surgery. If imaging is negative or discordant or if imaging suggests more than one abnormal parathyroid gland, then a conventional bilateral exploration is planned.
Fine Needle Aspiration
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