P-20 Primary hyperparathyroidism associated with maltoma of the thyroid gland: imaging challenges
Authors: Erturk Banu , Kaya Gürsan , Tuncel Murat , Ergin Meral Ilgaz , Haznedaroglu Ibrahim C , Uner Aysegul , Gurlek Alper 
Published: January 2024

Abstract

Introduction
Primary hyperparathyroidism (PHP) and malignancies are the most common causes of hypercalcemia. Nevertheless, PHP might be observed in coexisting with malignancies. We aimed to present a patient who underwent surgery for PHP and was diagnosed with thyroid MALToma.

Clinical Case
A 65-year-old female presented with fatigue for one year. The patient's medical history was unremarkable. On examination, thyroid gland was non-palpable. On laboratory, serum calcium (Ca), phosphorus (P) and parathormone (PTH) levels were 11 mg/dL (R: 8.8-10.6), 2.4 mg/dL (R: 2.5-4.5) and 157 pg/mL, respectively; vitamin-D was 23.63 µg/L and increased urinary Ca (400 mg per-day). She was euthyroid, and thyroid antibody elevated. Ultrasound (US) revealed multiple hypoechoic areas and a lesion (18×14 mm) in the vicinity of inferior right thyroid gland. Parathyroid scintigraphy revealed significant increase of metabolic activity posterior to the right lobe of the thyroid. She underwent right thyroid lobectomy thyroidectomy. Pathology revealed mucosa-associated lymphoid tissue (MALT) lymphoma of the thyroid. No parathyroid lesion noted. Then she was referred to our clinic. US revealed hypoechoic areas at remaining thyroid with no extra finding. We performed tru-cut biopsy from thyroid lesion. On immunochemistry, lymphoid cells were diffusely immunoreactive for CD3, CD5, CD20 and CD43 in the ymphocytes. Ki-67 index was 40%. Hence, the diagnosis of MALT lymphoma of the thyroid gland in the background of Hashimoto's thyroiditis. PTH staining of patient's previous pathology specimen was unremarkable. Pretreatment baseline 18F-flurodeoxyglucose PET/CT (FDG) revealed increased uptake (SUVmax: 5.1) in hypodense nodular structure in the posterior left lobe of the thyroid gland (Figure 1). FDG was suggestive of stage IE. Mild 18F-FCH uptake was observed suspected as parathyroid lesion next to the inferior left lobe. 4D-CT showed similar results. All imaging methods and we examined patient via US that revealed hypoechoic lesion with polar blood supply in the left lobe inferior (parathyroid adenoma). The patient were under rituximab 375 mg/m2 per week for 4 cycles. At the end of treatment, there were no sign of residual disease. Reoperation has not been planned due to the improvement of the patient's symptoms, and lymphoma with indolent course.

Conclusion
10% of PHP cases may have a concomitant malignancy, while association with lymphoma is even rarer. MALT lymphoma of the thyroid gland is a rare malignancy with an indolent course. The combination of these two rare conditions hard to orchestrate. As in our case, detection of parathyroid lesions becomes more difficult in the background of a low grade lymphoma. Indolent lymphomas have limited sensitivity with FDG. FCH could be more sensitive for discriminating parathyroid lesions and indolent lymphomas. It may be useful to confirm the localization of the PHP in such cases using multiple techniques involving FCH.Figure 1.Pre-treatment avid FCH uptake (A, B) and mild FDG uptake (C, D) related with thyroid MALToma; post-treatment complete remission shown in FDG (E, F); highly vascular paratracheal lesion at 4D-CT (G, H asterixis), the same lesion with mild FCH uptake (I-N arrows) and the same lesion with hypoechoic sonographic appearance evaluated as parathyroid adenoma (O arrow).