CASE OF THE WEEK – “Ectopic Parathyroid Adenoma in Neck by Tc-99m Sestamibi SPECT/CT Localization” by Dr ShekharShikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah

Ectopic Parathyroid Adenoma in Neck by Tc-99m Sestamibi SPECT/CT Localization

INTRODUCTION

Localization of parathyroid adenomas before surgery requires a multimodality approach to aid operative planning. Ectopic parathyroid adenomas are rare and are reported to account for 5–10% of cases of primary hyperparathyroidism (PHPT), which is often a diagnostic challenge for localization.

CASE REPORT

A 64-year-old lady with history of severe leg and low back pain of two months along with generalized body weakness and malaise. She has difficulty in standing of from sitting position.

History of a) HTN and on medication for last three years b) thyroidectomy and on thyroxine 100 microgram per day for last three years.

Biochemical parameters

The Sr. calcium (ionized) 6.1mg/dl (4.4-5.6), Sr calcium (total) 10.1 mg/dl (8.8-10.6). PTH 247 pg/ml (15-65)

Diagnosis of PHPT in view of raised serum calcium and parathyroid hormone (PTH) levels. Localization study was done with Ultrasonography, CT neck and MRI but did not able to localize any parathyroid adenoma.

REFERRED FOR 99mTc SESTAMIBI PARATHYROID SPECT-CT SCINTIGRAPHY
99mTc-MIBI PARATHYROID SPECT CT SCINTGRAPHY
EARLY AND DELAYED MIBI IMAGES OF NECK AND CHEST

It shows focal area of increased MIBI tracer uptakes (approximately AP 5.7 mm*transverse 6.7 mm*caudo-cranial 13.0 mm in size) seen below the level of hyoid bone on the left side of the midline posteriorly on initial images ( Better appreciated in SPECT-CT fused images as shown with arrow) and persistent tracer retention is seen in the same region on delayed washout (Better appreciated in SPECT-CT fused images as shown with arrow).

Thyroid gland shows small focal area of tracer uptakes in right thyroid be inferiorly on initial images and adequate washout pattern seen on delayed images.

No focal area of any abnormal tracer uptakes seen in mediastinal region.

99mTc-THYROID IMAGES

Small focal area of tracer uptake seen in right thyroid bed inferiorly. Marginal tracer uptakes in left side of thyroid bed (h/o of thyroidectomy and on T4).

THERE IS FOCAL METABOLICALLY ACTIVE PARATHYROID ADENOMA SEEN (APPROXIMATELY AP 5.7 MM*TRANSVERSE 6.7 MM*CAUDO-CRANIAL 13.0 MM IN SIZE) BELOW THE LEVEL OF HYOID BONE ON THE LEFT SIDE OF THE MIDLINE POSTERIORLY (ECTOPIC PARATHYROID ADENOMA IN NECK)

Small residual functioning thyroidal tissue in thyroidal bed as described above.

DISCUSSION

Ectopic parathyroid adenomas are rare and are reported to account for 5–10% of cases of PHPT. Pre-operative localization of hyperfunctioning parathyroid tissue is an essential component if minimally invasive surgery is scheduled. Parathyroid localization has improved with numerous imaging techniques, including sestamibi scintigraphy, ultrasonography, and four-dimensional CT.

Parathyroid scintigraphy using 99mTc-MIBI has been proven to be greatly effective for the diagnosis of adenomas, however, despite the relatively high accuracy of planar parathyroid imaging, intrathyroidal adenomas with low 99 mTc-MIBI uptake and ectopic adenomas may be overlooked.

SPECT/CT fusion imaging is increasing used, due to the three-dimensional information, it provides and the improved sensitivity for the detection and localization of hyperfunctioning parathyroid lesions. SPECT/CT can further enhance localization by providing better resolution of surrounding structures and has the added benefit of a more precise localization of ectopic and mediastinal parathyroid lesions.

We routinely do SPECT/CT imaging at 20 min post-tracer injection for more accurate anatomical localization the lesion. If it is posteriorly located, we can confirm a parathyroid lesion. Tc-99m pertechnetate thyroid imaging will be helpful in deciding if a lesion is due to an intrathyroidal lesion versus a thyroid nodule. If the lesion is in an ectopic location, more accurate anatomical localization is obtained. SPECT/CT is more reproducible as compared to ultrasound, which is operator dependent.

The single isotope, dual-phase technique is simple and easy to perform. It requires a single injection of sestamibi followed by early and delayed imaging. It takes advantage of the differential washout rates of sestamibi from the thyroid and the parathyroid glands. On delayed images, parathyroid lesions are easily visualized. This principle is based on the observation that sestamibi washes out more rapidly from the thyroid than from abnormal parathyroid tissue, where it is retained for a longer period of time. The retention in parathyroid lesions is assumed to be related to the presence of oxyphil cells, which are rich in mitochondria, and is the site of intracellular sestamibi sequestration.

CONCLUSION

Localization of parathyroid adenomas before surgery requires a multimodality approach to aid operative planning. This is particularly important in cases of ectopic parathyroid adenomas, in which the surgical approach has to be modified. The hybrid SPECT-CT imaging used in our patient has helped not only in diagnosis with confidence but also provided good information regarding location and anatomical details for operation.

Ectopic Parathyroid Adenoma in neck by Tc-99m Sestamibi SPECT/CT Localization

99mTcMIBI SPECT CT FUSED EARLY IMAGES

Ectopic Parathyroid Adenoma in Neck by Tc-99m Sestamibi SPECT/CT Localization” by Dr Shekar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah Ectopic Parathyroid Adenoma in Neck by Tc-99m Sestamibi SPECT/CT Localization” by Dr Shekar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah

There is focal metabolically active parathyroid adenoma seen (approximately ap 5.7 mm*transverse 6.7 mm*caudo-cranial 13.0 mm IN SIZE) BELOW THE LEVEL OF HYOID BONE ON THE LEFT SIDE OF THE MIDLINE POSTERIORLY (ECTOPIC PARATHYROID ADENOMA IN NECK)

 

99mTcMIBI SPECT CT FUSED DELAYED WASHOUT IMAGES

Ectopic Parathyroid Adenoma in Neck by Tc-99m Sestamibi SPECT/CT Localization” by Dr Shekar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah Ectopic Parathyroid Adenoma in Neck by Tc-99m Sestamibi SPECT/CT Localization” by Dr Shekar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah

There is focal metabolically active parathyroid
Adenoma seen (approximately ap 5.7 mm*transverse 6.7 mm*caudo-cranial 13.0 mm IN SIZE) BELOW THE LEVEL OF HYOID BONE ON THE LEFT SIDE OF THE MIDLINE POSTERIORLY
(ECTOPIC PARATHYROID ADENOMA IN NECK)

Ectopic Parathyroid Adenoma in Neck by Tc-99m Sestamibi SPECT/CT Localization” by Dr Shekar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah

Small residual functioning thyroidal tissue in thyroidal bed on 99mTc thyroid scan