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Spectrum of single photon emission computed tomography/computed tomography findings in patients with parathyroid adenomas
Address for correspondence: Dr. Bhagwant Rai Mittal, Professor and Head, Department of Nuclear Medicine, PGIMER, Chandigarh – 160 012, India. E-mail: brmittal@yahoo.com
This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article was originally published by Medknow Publications and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Primary hyperparathyroidism results from excessive parathyroid hormone secretion. Approximately 85% of all cases of primary hyperparathyroidism are caused by a single parathyroid adenoma; 10–15% of the cases are caused by parathyroid hyperplasia. Parathyroid carcinoma accounts for approximately 3–4% of cases of primary disease. Technetium-99m-sestamibi (MIBI), the current scintigraphic procedure of choice for preoperative parathyroid localization, can be performed in various ways. The “single-isotope, double-phase technique” is based on the fact that MIBI washes out more rapidly from the thyroid than from abnormal parathyroid tissue. However, not all parathyroid lesions retain MIBI and not all thyroid tissue washes out quickly, and subtraction imaging is helpful. Single photon emission computed tomography (SPECT) provides information for localizing parathyroid lesions, differentiating thyroid from parathyroid lesions, and detecting and localizing ectopic parathyroid lesions. Addition of CT with SPECT improves the sensitivity. This pictorial assay demonstrates various SPECT/CT patterns observed in parathyroid scintigraphy.
Keywords
Adenoma
ectopic
parathyroid
single photon emission computed tomography/computed tomography
sestamibi
INTRODUCTION
The parathyroid glands develop during the sixth week of gestation. The superior glands develop from the fourth brachial pouch and the inferior parathyroid glands develop from the third. Even though there are typically four parathyroid glands, approximately 10% of individuals have between five and seven glands, known as supernumerary parathyroid glands, and 2–3% of individuals have fewer than four glands. The location of the superior parathyroid glands is fairly constant. They are found at the junction of upper and middle third of thyroid gland, posterolateral to the cricothyroid junction in majority of the population. Occasionally, the superior gland may remain undescended near the hyoid bone, along the pharyngeal musculature described as a parapharyngeus, or anywhere along its route of descent adjacent to the carotid sheath. Rarely, they are intrathyroidal or retroesophageal. The inferior parathyroid glands have a more varied anatomy and are more commonly found in ectopic sites. They can be found anywhere between the aortic bifurcation to the mediastinum. The most common ectopic location of the inferior parathyroid gland is within the thymic capsule or the superior mediastinum.[1].
Primary hyperparathyroidism is characterized by the autonomous production of parathyroid hormone, resulting in hypercalcemia. It affects 1 in 500 women and 1 in 2000 men annually.[2] It occurs 2–3 times more frequently in women than in men. Hyperparathyroidism peaks in incidence in the fourth and fifth decades of life but can occur in young children and the elderly as well.[3] It is a severe, symptomatic disorder with skeletal, muscular and renal manifestations at a young age.[45] Normocalcemia is observed more often with frequency ranging from 50% in an earlier report[6] to 14% observed in a recent study.[5] Single adenoma is the most frequent etiology of primary hyperparathyroidism. Surgical treatment of hyperparathyroidism is successful in 95% of patients undergoing initial neck exploration.[7] Failure to find the parathyroidal lesion may be related to ectopia and anatomic variations in the location of the tumor. So far, the majority of parathyroid surgeons have held the consensus that preoperative localization studies are not indicated at initial exploration. However, this remains controversial. More recently, the better availability of preoperative parathyroid imaging techniques have made possible minimally invasive surgery, including unilateral neck exploration under local anesthesia[89] and endoscopic parathyroidectomy through a very small incision.[10] Accurate preoperative localization and intraoperative guidance are required to enable selective minimal surgery and to reduce the operative failure rate.[11] Moreover, repeated exploration is associated with a higher rate of complications, including recurrent laryngeal nerve paralysis and hypoparathyroidism.[12]
Anatomic imaging modalities including ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) have a relatively low sensitivity for detection of parathyroid adenomas.[13] Single-tracer dual-phase or the double-tracer subtraction parathyroid scintigraphy techniques provide high-quality imaging and reproducible scintigraphic findings. The previously used imaging approach combining Tl-201 and Tc99m subtraction scintigraphy showed only 45–75% sensitivity. Technetium-99m-MIBI scintigraphy has a higher target-to-background ratio and addition of single photon emission computed tomography (SPECT) improves the sensitivity to 90%.[14] Use of SPECT/CT helps to localize the ectopic parathyroid tissue. A combination of neck ultrasound and SPECT/CT has been shown to have incremental value over either technique alone and allows for selection of patients for minimally invasive parathyroid surgery.[15]
Source of Support: Nil
Conflict of Interest: None declared.
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