Preoperative imaging for a patient undergoing unilateral parathyroid surgery. Early (a) and delayed (b) Tc-99m-sestamibi scans showed slightly more persistent uptake in the right inferior central neck. These findings were concordant with the transverse (c) and longitudinal (d) ultrasound images, which revealed a hypoechoic lesion posterior to the lower portion of the right thyroid
Even though up to 85 % of patients with PHPT are potentially eligible for unilateral parathyroid surgery [2, 9], the actual candidate pool is reduced to 65–83 % of patients by limitations associated with preoperative localization techniques [9, 10]. Sestamibi scans, in particular, can have a sensitivity as low as 50 % in some centers [9, 18]. These rates improve significantly when the imaging is performed in high-volume specialty centers, where up to 80–90 % of patients may have localizing sestamibi scans [18, 19]. Localization can also be improved when imaging studies are combined. Single-gland disease has been confirmed in up to 96–99 % of patients who have concordant (colocalizing) sestamibi and ultrasound studies, while up to 17 % of patients with discordant imaging have multigland disease [1, 20].
Some authors perform unilateral surgery when the ultrasound and sestamibi results are concordant [14, 20], while others will perform a UNE if at least one study indicates which side to explore first [15, 20]. Patients with discordant or nonlocalizing studies should be considered for BNE . Patients at risk for multigland disease, including those with familial or syndromic causes of HPT (MEN syndromes), secondary or tertiary HPT, or a history of lithium use, should undergo planned bilateral exploration [3, 21].
As mentioned previously, numerous operative variations have been described for unilateral parathyroid surgery. Minimally invasive radioguided and endoscopic parathyroid surgery are specifically addressed elsewhere in this text, so the procedure described in this chapter will focus on open unilateral surgery without gamma probe or video assistance.
Reducing the scar size and improving the cosmetic outcome of parathyroid surgery is one of the advantages of unilateral surgery. Therefore, careful attention is given to planning the incision length and location. Marking the incision site while the patient is sitting up in the preoperative holding area ensures that the scar will be concealed in the most favorable naturally occurring skin crease . Most open unilateral explorations can be performed through midline incisions less than 4 cm, with many authors routinely reporting incision lengths of 2–3 cm [11, 18, 23]. In addition to being more cosmetically favorable, a midline incision permits exploration of the contralateral neck should conversion to a bilateral exploration be required .
The procedure can be accomplished with the patient sedated  or under general anesthesia. General anesthesia permits intraoperative recurrent laryngeal monitoring, if desired. The patient is positioned supine on the operating table with minimal or no neck extension. Rotating the table 180° so the patient’s lower extremities are facing the anesthesia team allows IV access in the patient’s foot for IOPTH assessment . Once the patient is in the final operative position, a surgeon-performed ultrasound is used to confirm the location of the suspected adenoma and guide the subsequent dissection . The incision site is then infiltrated with an epinephrine-containing anesthetic solution. The skin is incised and the platysma is divided. Subplatysmal flaps are not necessary . The strap muscles are separated in the midline, exposing the thyroid isthmus. Care is taken to maintain absolute hemostasis, as any bleeding from superficial tissue layers can obscure the critical visualization of deeper structural details. Attention is then directed to the side of the neck predicted by preoperative imaging to harbor the hyperfunctional parathyroid tissue. The strap muscles are bluntly elevated off the anterior and lateral aspect of the thyroid. The thyroid is then retracted medially, taking great care not to conceal a parathyroid gland under the retractor blade, and the process of identifying the abnormal gland(s) begins.
Most parathyroid glands reside in predictable locations in the central neck . Guided by the preoperative imaging, and using meticulous technique, the surgeon begins searching for the most likely abnormal gland. The superior glands are more constant in location. They are usually found behind the superior aspect of the thyroid gland near where the recurrent laryngeal nerve passes under the inferior constrictor, within a 2 cm area centered 1 cm cranial to the junction between the recurrent laryngeal nerve and the inferior thyroid artery , and are always dorsal to the plane of the recurrent laryngeal nerve. The location of the inferior parathyroid glands is more variable. They are typically located within 1 cm of the inferior aspect of the thyroid gland, anterior to the plane of the recurrent laryngeal nerve, but may be intimately associated with the thymus or thyro-thymic tract in up to 26 % of patients [26, 27].
The superior gland is revealed by retracting the thyroid gland ventrally and medially, exposing the posterior aspect of the thyroid lobe and the paratracheal region. This exposure can usually be accomplished without disrupting of the middle thyroid vein. Occasionally, however, the middle thyroid vein and superior pole vessels will need to be divided to fully access this space. The inferior parathyroid gland may be found by gently dissecting the soft tissue just below the inferior pole of the thyroid gland, or it may be identified dorsal to the gland by gentle retraction of the thyroid lobe.
Surgeons must be able to visually distinguish a normal from abnormal parathyroid gland. Normal parathyroid glands are typically flat, with a light brown to tobacco color, and measure 3–8 mm long with an average weight of 40 mg . They are usually surrounded by or capped with fat. Parathyroid adenomas are typically larger, more rounded, rubbery, and a darker red-brown in color.
The presence of an enlarged parathyroid gland may be heralded by areas of fullness or bulging of the peri-thyroidal fat . Gently spreading the surrounding fat may help reveal the enlarged gland. Once identified, blunt dissection is used to separate the adenoma from the surrounding soft tissue, until only the vascular pedicle remains attached to the gland. Soft tissue adherent to the capsule of the gland may be grasped to facilitate retraction and dissection, but care should be taken to avoid grabbing or excessive manipulation of the gland itself, as this may rupture the gland or stimulate release of stored parathyroid hormone and alter subsequent IOPTH levels . The vascular pedicle feeding the adenoma is then either transected with electrocautery or ligated with vessel clips and sharply divided if it is near the recurrent laryngeal nerve.
Though not uniformly performed by all authors [6, 10], complete UNE implies that after removal of the parathyroid adenoma identified on preoperative imaging, the second ipsilateral gland is identified and sometimes biopsied [9, 14, 24]. The decision to perform a complete unilateral dissection or terminate the operation after identifying only one adenoma depends on the surgeon’s philosophy, the preoperative imaging, and the availability of IOPTH assessment (Fig. 19.2). Some surgeons feel that if preoperative imaging studies, especially when concordant, match the operative findings, the operation can be concluded after removing the adenoma (with or without identifying a second ipsilateral gland), and that further assessment is not necessary . Other authors suggest that identification of a second, normal gland still requires biochemical confirmation (using an IOPTH assay) that all the hyperfunctional parathyroid tissue has been removed . In cases where a second gland cannot be identified or appears abnormal, or when the IOPTH levels fail to decrease appropriately, bilateral exploration is warranted . The procedure on the contralateral side is performed through the same incision in an identical manner as the initial side, with a goal of identifying all four parathyroid glands (see following chapter).
Intraoperative parathyroid hormone assay equipment (Future Diagnostics, Wijchen, Netherlands)
Once all the hyperfunctional parathyroid tissue has been removed, the surgical field is irrigated, hemostasis assured, and half a sheet of Surgicel (Ethicon, Inc., Somerville, NJ) is placed into the wound bed. The strap muscles are either reapproximated in the midline with a single 3-0 Vicryl (Ethicon, Inc., Somerville, NJ) figure-of-eight suture  or left open. The subcutaneous tissue is closed with buried interrupted 4-0 Vicryl (Ethicon, Inc., Somerville, NJ) sutures and the skin edges are closed with tissue adhesive and a single transverse Steri-Strip (3M Corporation, St. Paul, MN) (Fig. 19.3). No drains or external sutures are required [29–31]. Patients are generally discharged on the same day of surgery with an oral calcium regimen [32, 33].
The reported cure rate of 96–98 % after unilateral parathyroid surgery is identical to that of bilateral exploration in appropriately selected patients [6, 9, 14], and has been shown to be durable . While some authors do not routinely perform an IOPTH assay in unilateral surgery, others have shown improved outcomes when this assessment is utilized [1, 10]. Rajaei et al. evaluated the second ipsilateral gland in 809 patients, and found that 13 % of procedures would have resulted in failure if assessment of the second gland alone was used to determine the presence of multigland disease, while the cure rate for UNE with IOPTH assessment was 98.5 % . IOPTH assessment, which can now be performed in the operating room in as little as 8 min , has been specifically recommended in cases where localization studies are discordant or only one study is performed .
Conversion to bilateral surgery occurs in 6–14 % of planned unilateral explorations [10, 14, 15]. These conversions typically result from failure of the IOPTH levels to drop appropriately, concern over multigland disease after inspection of the second ipsilateral parathyroid gland, failure to identify the desired gland(s), or other unexpected but concerning intraoperative findings [10, 14, 15].