Introduction
Primary hyperparathyroidism (PHPT) is a clinical condition characterized
by elevated serum parathyroid hormone (PTH), followed by increased serum
calcium (Ca). Patients with PHPT frequently manifest symptoms such as
hypercalcemia, anorexia, nausea, and nephrocalcinosis. The treatment for
PHPT used to be a total parathyroidectomy, but PHPT is usually caused by
a single parathyroid adenoma (PTA)(1, 2), and selective
parathyroidectomy has been recently preferred for the treatment of
single adenomas as a less invasive option(3, 4).
For a successful selective
parathyroidectomy, accurate
imaging techniques are required for the preoperative localization of
PTAs. Ultrasonography and technetium 99mTc-sestamibi scintigraphy have
often been accepted as first-line imaging to localize PTAs. When
first-line imaging fails to localize the parathyroid lesion, or PHPT is
recurrent or persistent after surgery, computed tomography (CT) and
magnetic resonance imaging (MRI) are considered as second-line imaging
techniques (1, 5). Recently, the multiphasic CT (4D CT) has made it
possible to identify PTAs through their hypervascular perfusion pattern
compared with lymph nodes and thyroid gland(5), however CT has the
disadvantage of ionizing radiation.
MRI has the advantage of lack of ionizing radiation, and with the
introduction of high field magnetic systems, the use of MRI for the
localization of parathyroid adenomas has been re-assessed as a
supplemental imaging modality. The sensitivity of 1.5T MRI for the
detection of PTAs was reported to be 43%–71%(6-8), but since 3T
scanners were introduced into clinical practice in the early 2000s, the
higher signal-to-noise and contrast-to-noise ratios have improved the
sensitivity of MRI to 97.8%.(1) However, some limitations remain
because the MR appearance of PTAs overlaps considerably with those of
cervical lymph nodes and an ectopic thyroid gland, which leads to
difficulties in distinguishing PTAs from other structures in the neck.
The measurement of the apparent diffusion coefficient (ADC) value in
diffusion-weighted imaging (DWI) has been reported to be helpful in
distinguishing parathyroid tissues from other soft-tissue structures of
the head and neck region.(9) Single-shot echo-planar imaging (SS-EPI)
has been the most widely used DWI sequence, but SS-EPI suffers from
susceptibility artifacts which manifest as geometric distortion and
image blurring,(10) and the detection of PTAs by DWI thus remains
challenging. To overcome this weakness, readout-segmented echo-planar
imaging (RS-EPI) was developed; with this imaging modality, there is a
substantial reduction in the distortion and blurring caused by T2* decay
during the readout(11, 12). RS-EPI is expected to improve the diagnostic
accuracy of detecting PTAs on DWI as it provides less distortion, and
its advantages are reported in some organs including the head and
neck(13-15).
However, to our knowledge, there is no literature focusing on the
usefulness of RS-EPI for the localization and distinction of PTAs. We
conducted the present retrospective study to determine whether RS-EPI
can reduce image distortion and improve the lesion identification in
PTAs compared to SS-EPI, and to determine whether PTAs can be
differentiated from other soft-tissue structures of the head and neck
region by using the ADC value.