Advantages of hybrid SPECT-CT imaging in preoperative localization of parathyroid glands in a patient with secondary hyperparathyroidism. A case report.

BACKGROUND: Secondary hyperparathyroidism is a frequent complication of chronic renal failure. Patients resistant to pharmacotherapy are candidates for parathyroidectomy. Invasiveness of surgical treatment can be minimized by precise preoperative localization of parathyroid glands. Imaging modalities routinely used for this purpose are ultrasonography and MIBI-Tc99m scintigraphy. CASE REPORT: Our case report shows advantages of co-registered computer tomography and conventional SPECT imaging (SPECT/CT) in a patient with advanced secondary hyperparathyroidism successfully treated with surgery.
RESULTS: Hybrid SPECT/CT parathyroid imaging enables better surgical planning and is superior to conventional scintigraphy.

Background

Hyperparathyroidism is a common endocrinological disorder. Primary hyperparathyroidism (PHPT) typically results from solitary parathyroid adenoma (80% of cases) and occurs in 0.1–0.35 percent of population [1-3]. Secondary hyperparathyroidism (SHPT) frequently complicates the late stages of chronic renal failure – it is encountered in 20–25% of chronically dialyzed patients [4]. The most important method of treatment of PHPT is surgical resection of hyperactive parathyroid gland, whereas in SHPT it is one of the options reserved for patients with hyperparathyroidism resistant to pharmacological therapy [5].

Effectiveness of surgical procedure is highly dependent on precise preoperative localization of lesions. A 99mTc-MIBI SPECT and neck ultrasound examination are approved as standard procedures for localizing abnormal parathyroid glands [6,7]. Sensitivity of ultrasound combined with scintigraphy in detecting single parathyroid adenomas reaches 95 percent [8,9], while in SHPT there are discrepancies in reported sensitivity of scintigraphy – it varies from 25 to 74 percent, which is much lower than in PHPT [9-12]. The role of routine MIBI scintigraphy in SHPT is still discussed, however in positive cases it can provide a surgeon with valuable information.

Several (from 5 to 6.7) percent of operated patients both with PHPT and SHPT suffer from persistent disease [13,14] after unsuccessful operation.

Ultrasound examination is useful in localizing eutopic adenomas and in patients with normal thyroid gland, while scintigraphy more precisely detects ectopic adenomas and is more valuable in the presence of a nodular goiter [15,16]. Some authors report that diagnostic usefulness of ultrasonography and scintigraphy is similar, but still complementary [17,18]. Hybrid SPECT-CT imaging, which integrates scintigraphic data with radiological image (computer tomography) gained high popularity and availability in recent years. However, the number of published papers evaluating clinical utility of SPECT-CT in preoperative mapping of hyperfunctioning parathyroid glands in SHPT exclusively is still limited [19-21]. Available articles usually encompass patients from both groups - PHPT and SHPT, predominantly the former [22-24].

Case Report

Our case report describes a patient who was operated due to SHPT and underwent subtotal parathyroidectomy (three and a half out of four parathyroid glands were removed) in January 2012.

In 2000, patient suffered from necrotic pancreatitis, which was complicated by renal failure. He has been hemodialyzed since 2008. In 2011, he was diagnosed with SHPT. Before the surgery, his laboratory parameters were the following: parathormone 3866 pg/ml [normal values 10–55 pg/ml], calcium 9.26 mg/dl [8.5–10.2 mg/dl], creatinine 3.57 mg/dl [0.7–1.3 mg/dl]. After surgery, parathormone level dropped to 6 pg/ml.

We performed 99mTc-MIBI scintigraphy before the surgery: traditional planar, dual-phase imaging and additional SPECT-CT imaging for precise preoperative localization of disease sites. Planar images (Figure 1) revealed three out of four parathyroid glands depicted in SPECT/CT. Moreover, SPECT/CT provided additional information about anatomic localization of glands: superior parathyroids were situated behind the mid-lower parts of thyroid lobes, close to the esophagus (Figure 2A), while inferior glands – near the lower poles of thyroid lobes, close to the trachea (Figure 2B). Left inferior parathyroid gland is also presented on cross-section images (Figure 3A, 3B). No ectopic glands were detected.

Figure 1.

Dual phase 99mTc-MIBI planar scintigraphy of parathyroid glands. On the left: early phase (after 10 minutes post injection of tracer) – showing nonspecific uptake in thyroid and parathyroid glands. On the right: late phase (after 120 min) – wash-out of activity from thyroid and retention in three hyperfunctioning parathyroid glands (two inferior and left superior), one gland (right superior) is not visible.

Figure 2.

Two images of late phase 99mTc-MIBI SPECT/CT clearly visualizing tracer retention in two inferior (A) and two superior (B) hyperactive parathyroid glands.

Figure 3.

SPECT/CT and CT alone of the same cross-section, showing left inferior parathyroid. The best diagnostic performance is achieved by combination of detailed morphological image (CT) and functional, scintigraphic map (SPECT/CT).

The images are presented above.

Precise and thorough information regarding localization of lesions in our patient was delivered to the surgeon before the operation. Location of all four glands was fully confirmed by surgical exploration. A 3-mm fragment of left inferior parathyroid was left. Additionally, a tubercle of Zuckerkandl was found on the right side and removed.

Discussion

An accurate preoperative mapping of hyperfunctioning parathyroid glands, both in PHPT and SHPT, shortens the duration of surgery, minimizes its invasiveness and decreases number of patients with recurrences, particularly in case of ectopic gland location [25].

Wimmer compared MIBI-SPECT/CT, CT alone and MIBISPECT alone in patients with multiglandular disease – abnormal glands were detected in 46.7%, 36.7% and 13.3% of patients, respectively [26]. Oksuz obtained different results in a group of patients with PHPT and SHPT – sensitivity per lesion was 69 percent for planar imaging and 95 percent for both SPECT and SPECT-CT [22]. In the study by Kim, including 19 patients with PHPT and 5 patients with SHPT, SPECT/CT demonstrated 100% sensitivity per patent and had significantly better sensitivity than planar scintigraphy, SPECT and conventional imaging [23].

A 99mTc-MIBI SPECT imaging provides good localization of parathyroid glands, although our experience of cooperation with surgeons highlights the benefits of using SPECT-CT. This concerns both PHPT and SHPT. However the number of papers describing the secondary disease is small, which means that further investigation is needed to establish the value of SPECT/CT in this group of patients.

In our patient, planar imaging was insufficient, as it did not reveal all parathyroids. Furthermore, information gained from SPECT/CT allowed for their quick intraoperative localization thanks to detailed reports regarding the relation of lesions to anatomic landmarks, unavailable in both SPECT alone and planar imaging.

Additionally, effectiveness of surgery can be further improved with intraoperative detection of parathyroid glands using a hand-held gamma probe [27,28].

Conclusions

Hybrid SPECT/CT parathyroid imaging is superior to performing SPECT imaging alone. It enables better surgical planning and improves its outcome.