Short Scientific Communication—Endocrine Surgery

4D MRI for the Localization ofParathyroid Adenoma: A Novel Methodin Evolution

Otolaryngology–Head and Neck Surgery2016, Vol. 154(3) 446–448� American Academy ofOtolaryngology—Head and NeckSurgery Foundation 2015Reprints and permission:sagepub.com/journalsPermissions.navDOI: 10.1177/0194599815618199http://otojournal.org

Shlomo Merchavy, MD1,2, Judith Luckman, MD3,Michal Guindy, MD, MPA3, Yoram Segev, MD3, and Avi Khafif, MD1

No sponsorships or competing interests have been disclosed for this article.

Abstract

The sestamibi scan (MIBI) and ultrasound (US) are used forpreoperative localization of parathyroid adenoma (PTA),with sensitivity as high as 90%. We developed 4-dimensionalmagnetic resonance imaging (4D MRI) as a novel tool foridentifying PTAs. Eleven patients with PTA were enrolled.4D MRI from the mandible to the aortic arch was used.Optimization of the timing of image acquisition was obtainedby changing dynamic and static sequences. PTAs were identi-fied in all except 1 patient. In 9 patients, there was a com-plete match between the 4D MRI and the US and MIBI, aswell as with the operative finding. In 1 patient, the adenomawas correctly localized by 4D MRI, in contrast to the USand MIBI scan. The sensitivity of the 4D MRI was 90% andafter optimization, 100%. Specificity was 100%. We con-cluded that 4D MRI is a reliable technique for identificationof PTAs, although more studies are needed.

Keywords

4D MRI, parathyroid adenoma, Sestamibi scan, ultrasound,minimally invasive surgery

Received June 19, 2015; revised October 14, 2015; accepted October

29, 2015.

The incidence of primary hyperparathyroidism (PHPT) is

0.2% to 0.5% in the general population.1 The most

common cause of PHPT is sporadic solitary adenoma

(85%), followed by 4-gland hyperplasia (9%) and double ade-

noma (3%).2,3 In the last decade, due to the high sensitivity of

the ultrasound (US) and sestamibi (MIBI) scan (.90%),4 bilat-

eral neck exploration is currently being replaced by minimally

invasive parathyroidectomy (MIP).4,5 MIP is associated with

benefits of limited cervical dissection, smaller surgical incision,

less postoperative pain, and decreased cost due to reduced hos-

pital lengths of stay.5,6 Although US and MIBI scan are reliable

modalities, there are cases in which they fail to demonstrate the

adenoma. Other modalities, such as computed tomography (CT)

and magnetic resonance imaging (MRI), have demonstrated low

sensitivity and specificity and therefore are not routinely used in

patients with PHPT with negative US or MIBI scans.3 Four-

dimensional (4D) CT was lately reported as an effective tool in

identifying hidden adenomas,7 but it is associated with high

radiation exposure.

We developed a new MRI protocol: 4D MRI as a novel

tool for identifying parathyroid adenoma.

Methods

This study was approved by the local ethics committee of

Assuta Medical Center, Tel Aviv, Israel. Patients were

enrolled in the study if they underwent MIP in the Assuta

Medical Center between September and November 2014.

All patients had localization of the adenoma by US and

MIBI scan prior to surgery. MRI was performed on a 1.5-T

Espree Siemens machine. Standard sequences were per-

formed, including T1 and T2 TSE axial sequences and T2

MEDIC sequences (GE T2), from the mandible to the thor-

acic inlet, as well as coronal and sagittal and coronal T1

and STIR. A dynamic study was performed. For the first 4

patients, different dynamic magnetic resonance angiogram

sequences were performed, including TWIST and bolus

studies. The resolution in these sequences was inadequate

to differentiate between the adenoma and the surrounding

soft tissues. Therefore, the protocol was adjusted. The final

technique used was 1.5-mm T1 vibe sequences (GE T1) in

axial planes, scanned in dynamic fashion every 13 seconds

for 10 times, starting without contrast and continuing with

a gadolinium contrast that was injected by an automatic

injector. Rate of injection was 4 mL/s with a total of 12 to

20 mL of Gadovist (gadobutrol) or Dotarem (gadoterate

meglumine), depending on patient weight. The imaging

1ARM Center of Otolaryngology Head and Neck Surgery, Assuta Medical

Center, Tel Aviv, Israel2Faculty of Medicine in the Galilee, Bar-Ilan University, Safed, Israel3Imaging Department, Assuta Medical Center, Tel Aviv, Israel

This article was presented at the 2015 AAO-HNSF Annual Meeting & OTO

EXPO; September 27-30, 2015; Dallas, Texas.

Corresponding Author:

Shlomo Merchavy, MD, Department of Otolaryngology–Head and Neck

Surgery, Padeh Medical Center, 15208 Poriya, Israel.

Email: Merchavy@gmail.com

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studies were analyzed by a dedicated head and neck neu-

roradiologist who was blinded to the US and MIBI scan

results.

Surgery was terminated when 2 parameters were achieved:

histologic finding of hypercellular parathyroid gland on

frozen section reading and decrease of intraoperative para-

thyroid hormone levels (.50%) 10 minutes after removal.

Results

Eleven patients (8 women) aged 37 to 73 years (mean, 58

years) enrolled in the study after undergoing successful

removal of parathyroid adenoma by MIP, with subsequent

normalization of calcium and parathyroid hormone levels.

Parathyroid adenomas were identified by 4D MRI in all

except 1 patient (false negative). As mentioned, due to inad-

equate resolution and 1 false negative (9%) among the first

4 patients, the protocol was adjusted, and fast T1 vibe

sequences (GE T1) in the axial plane were obtained before

injection and every 13 seconds for 10 sequential scans.

Adenomas were visualized on the static images (Figure 1)

and dynamic scans and demonstrated fast enhancement after

26 to 30 seconds (Figure 2). False positives did not occur

after optimization.

In 9 patients, there was a complete match between the

4D MRI and the US and MIBI and with the operative find-

ing. In 1 patient, the US and MIBI wrongly identified a left

thyroid nodule as a parathyroid adenoma. However, during

surgery, the adenoma was identified on the right side, as

shown by the 4D MRI.

The positive predictive value of the 4D MRI was 91%.

In the final protocol, after optimization, sensitivity was

100%.

Discussion

In our study, we found that 4D MRI is a reliable diagnostic

tool for the evaluation of parathyroid adenoma.

To enable MIP, accurate localization is required. US and

MIBI scans are the main imaging modalities and commonly

used in combination to localize the diseased gland.

US is a noninvasive, inexpensive tool to localize parathyr-

oid adenoma. However, its sensitivity and specificity are con-

troversial, since they are operator dependent. Siperstein et al

reported a US sensitivity of 65% to 74%.8 In our study, US

sensitivity was 91%. Our findings agree with Zawawi et al9

and Bachar et al,3 who reported a sensitivity of 90% and con-

cluded that an experienced radiologist can precisely locate

parathyroid adenoma in 90% of patients with PHPT.

The MIBI scan was reported to have high sensitivity and

specificity. Our findings agree with Denham et al, 4 who

reported 90% sensitivity. Still, the MIBI scan has several

limitations, since thyroid nodules or other hyperactive meta-

bolic tissues (eg, metastatic lymph node) may mimic para-

thyroid tissue. The MIBI scan, even when incorporated with

Figure 2. T1 axial image showing the same lesion avidly enhanced30 seconds postinjection.

Figure 1. T1 axial image showing left inferior thyroid lesion in theearly arterial phase with mild enhancement.

Merchavy et al 447

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single-photon emission CT, does not always give a detailed

anatomic localization of the adenoma and will rarely reveal

a double adenoma or hyperplasia of 4 glands. As mentioned,

4D CT has recently been reported as a novel tool to identify

hidden parathyroid adenoma.7,10 Table 1 compares 4D CT

and 4D MRI.

If the results of the US and MIBI scan disagree or if one

of the modalities did not localize the adenoma, further ima-

ging modalities are usually preformed (CT, MRI, angiogra-

phy). In this article, we describe a new 4D MRI protocol as

another option for identification of adenomas not found by

US, MIBI scan, or both.

Conclusion

A new tool for identification of parathyroid adenomas was

developed. Although initial results are promising, more

studies are needed to compare 4D MRI results with surgical

findings in patients with negative MIBI and US.

Author Contributions

Shlomo Merchavy, design the study, analyzed the data, writing

the manuscript. approval of final version of manuscript, agree to

be accountable for all aspects of the work; Judith Luckman, writ-

ing the manuscript and data analysis, critically reviewing manu-

script. approval of final version of manuscript, agree to be

accountable for all aspects of the work; Michal Guindy, study

design conception, critically reviewing manuscript. approval of

final version of manuscript agree to be accountable for all aspects

of the work; Yoram Segev, study design conception, writing the

manuscript, approval of final version of manuscript. agree to be

accountable for all aspects of the work; Avi Khafif, study design

conception, writing the manuscript, critically reviewing manu-

script, critically reviewing the manuscript, agree to be accountable

for all aspects of the work.

Disclosures

Competing interests: None.

Sponsorships: None.

Funding source: None.

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Table 1. Comparison of 4D MRI vs 4D CT.

4D Pros Cons

MRI High sensitivity and specificity

No radiation exposure

Contraindications: pacemaker, severe claustrophobia, metallic foreign body

Experienced neuroradiologist required

More artifacts due to motion and swallowing

CT Claustrophobia is not contraindicated in CT

Fewer artifacts due to shorter time of examination

High radiation exposure

Abbreviations: 4D, 4-dimensional; CT, computed tomography; MRI, magnetic resonance imaging.

448 Otolaryngology–Head and Neck Surgery 154(3)

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