Thyroid Science 5(4):1-4, 2010	www.ThyroidScience.com
Case Reports
FDG-PET/CT Visualizes a

Case of Primary Hyperparathyroidism in a

Patient with Gastrointestinal Stromal Tumor

Laura Evangelista,1,2 Anna Rita Cervino,1

Michele Gregianin,1 Giorgio Saladini1

1Department of Radiotherapy and Nuclear Medicine Service,

Istituto Oncologico Veneto, Padova, Italy.

2Department of Biomorphological and Functional Sciences,

University Federico II, Napoli, Italy

Correspondence author: Laura Evangelista

Istituto Oncologico Veneto, IOV, I.R.C.C.S., Via Gattamelata, 64, 35128 Padova, Italy

Tel: +39 3396687579; Fax: +39 049 821 2205 laura.evangelista@tin.it

Received: April 8, 2010

Accepted: April 13, 2010

Abstract. Background. Positron emission tomography/computed tomography (PET/CT) is used in clinical practice above all other tests to define the status of oncological disease. The predominant use of PET/CT is due to its use of 18F- fluorodeoxyglucose (FDG) to map cellular glucose metabolism. Some benign clinical conditions are also detected with FDG-PET/CT. These include inflammatory or hypermetabolic processes. Parathyroid adenoma is the most common cause of primary hyperparathyroidism, and nuclear medicine is already used to locate adenomas and to guide surgery for their removal. The utility of PET/CT with 11C-meth
ionine for parathyroid disorders is well-documented in the research literature, while the usefulness of PET/CT with 18F-FDG is not clear. Case Presentation. We reported a case of a patient without specific symptoms for primary hyperparathyroidism, with a borderline high value of parathyroid hormone and a positive finding of parathyroid disease with PET/CT using 18F-FDG. Conclusion. PET/CT with 18F-FDG is useful in iden
tifying parathyroid adenomas, and the techniques can be used to precisely clarify the nature of suspected nod
ules close to thyroid gland.

Keywords • Adenoma • Computerized tomography • 18F-Fluorodeoxyglucose • 11C-Methionine • Oncological disease • Parathyroid hormone • Parathyroidism • Positron emission tomography

Background

The pathogenesis of primary hyperparathyroidism is due to an adenoma in 85% of cases. In a small per
centage of cases, hyperparathyroidism involves multi endocrine syndrome (MEN). The diagnosis of pri
mary hyperparathyroidism is based on hypercalcaem
ia and elevated levels of parathyroid hormone.

The flow-chart for concluding that parathyroid pathologies are present begins with a biochemical evaluation and thereafter with diagnostic imaging. 99mTc-MIBI-guided detection of abnormal parathyroid glands in primary hyperparathyroidism has become a popular and effective technique, especially to allow the performance of minimal surgery.[1]

Combined positron emission tomography/com
puted tomography (PET/CT), using 11C-methionine as the alternative radio-labelled amino acid tracer a
gent, has already been demonstrated to play an im
portant role in localating pathological parathyroid glands.[2-5] On the other hand, Lange-Nolde et al. [6] suggested that PET with 18F-DOPA (3-,4-dihydrox
y-6-(18)-F-fluorophenylalanine), another radiolabel
led tracer, is not useful in the detection of parathyroid adenomas in patients with primary hyperpara
thyroidism. Today, however, the role of 18F-FDG PET/CT in identifying parathyroid pathologies is still not clear.

Case presentation

A 37-year-old female who had a history of gastrointestinal stromal tumor and was treated with surgery in July 2009 was referred to our Department of Nuclear Medicine for evaluation of the disease state. She underwent PET/CT exam for post-surgery evaluation. At the time of imaging, she reported hair loss, trembling hands, split nails, and irregular men
struation. The PET/CT examination performed with 18F-FDG showed a small area near and posterior to the left lower pole of her thyroid gland. The small area was moderately hypermetabolic and had a max
imum Semiquantitative Uptake Value (SUV max) of 6.0 (Figure 1A).

The biochemical evaluation showed a serum parathyroid hormone level of 76 ng/L (reference val
ues 9-to-55 ng/L) and reference values of serum cal
cium and phosphate. For further evaluation, the pa
tient underwent a neck ultrasound exam. This reveal
ed the presence of an ipoechoic nodule with structural morphology similar to the parathyroid gland and in the same site.

Finally, based on clinical and diagnostic findings, a diagnosis of primary hyperparathyroidism was made. Thereafter, for the localization of the adenoma, a 99mTc-sestamibi parathyroid dual-phase scintigraphy was performed. This revealed an area with high up
take (Figure 1B) in the same place shown by the PET/CT images. These data demonstrate the utility of 18F-FDG uptake in identifying the site of the ade
noma.

Discussion

PET/CT with 18F-FDG is an imaging modality that has been in widespread use in recent years. The procedure is used especially in the oncological field, but also in the cardiovascular and neurological fields. The increased glucose metabolism of all pathological processes can be visualized by FDG-PET.

Primary hyperparathyroidism is due mainly to adenomas of the parathyroid glands. The increased number of parathyroid cells elevates glucose metab
olism. Parathyroid adenomas, as incidental findings are not often detected during PET examinations, but other incidental clinical conditions (e.g. breast cancer, thyroid cancer, colon inflammatory disease, etc.) are usually depicted.[7-9] In fact, the research literature contains only one case, by Kim et al.,[10] that demon
strated an intra-thyroidal parathyroid adenoma dis
covered by FDG-PET.

The patient whose case we report here had a history of GIST, a rare cancer that affects the diges
tive tract or nearby structures within the abdomen. Followup post-surgery evaluation was the reason the patient had an evaluation with FDG-PET/CT.

In the literature, Papillon et al.[11] reported a case of a patient with MEN-1 and associated GIST. They conjectured that the patient's GIST arose indepen
dently by a mechanism unrelated to the MEN-1 gene.

Precise identification of the location of a sus
pected nodule close to the thyroid gland can be useful in deciding whether or not further diagnostic tests are appropriate. Such decisions are particularly important in the management of oncological patients. The rea
son is that it is well known that oncological path
ologies can induce a hypercalcaemia, as can parathy
roid adenomas. It is necessary, then, to differentiate between oncological pathology and parathyroid ade
nomas as the source of patients' hypercalcemia.

Conclusion

Should 18F-FDG be used as an alternative to 11C-methionine to detect parathyroid adenomas? In view of the clinical flow-chart, this is questionable for two reasons,: first is the cost/benefit ratio, as PET/CT is more expensive than other imaging modalities; second is the proved diagnostic utility of scintigraphy with 99Tc-sestamibi. Far more data from studies are necessary to clearly delineate the advantages of FDG-PET/CT compared to other procedures in the diagnosis of primary hyperparathyroidism. However, nowadays, FDG-PET/CT is considered the best tech
nique for oncological evaluations, and in the near future, it may become clear that this imaging techni
que also could be employed in the diagnosis of other clinical conditions including parathyroid adenomas.

References

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