Thyroid Tuberculosis Depicted by 18 F-FAPI PET/CT

Abstract

Thyroid tuberculosis is a rare condition that is difficult to diagnose and may be suspected of being a malignant tumor. We report a case of thyroid tuberculosis in a 54-year-old woman that mimicked thyroid cancer on ultrasound, with a 18 F-FAPI PET/CT scan showing intense 18 F-FAPI uptake in the thyroid lobe, right neck lymph node, and celiac lymph nodes.

Keywords: 18F-FAPI; PET/CT; thyroid tuberculosis; tuberculosis.

FIGURE 1

A 54-year-old woman presented with a right cervical mass that had been present for one year. During this period the mass had grown gradually, accompanied by no pain, fever, or other discomfort. She then underwent a cervical color ultrasound which showed TI-RADS 4b in the right thyroid lobe due to 2 irregular, hypoechoic nodules with no obvious boundary, an uneven internal echo with punctured calcification, and a diameter >1 cm. This right neck mass was considered to be metastatic lymph nodes from the thyroid. After admission to the hospital, a biopsy of the right enlarged cervical lymph nodes indicated the diagnostic possibility of sarcoidosis or tuberculosis. In view of the ultrasound findings, she was enrolled in our clinical trial (Registration number: ChiCTR2400089382) for a ¹⁸F-FAPI PET/CT scan. The MIP (A) revealed multiple hypermetabolic lesions in the thyroid (black arrow) and neck and abdomen (blank arrow). In the axial views of the PET/CT (B), 3 nodules showed intense ¹⁸F-FAPI uptake in the thyroid lobe. The SUVmax of the lesions was 18.99, 21.55, and 9.94 in the upper location of the right thyroid lobe (long white arrow), lower location of the right thyroid lobe (short white arrow), and thyroid isthmus (dotted white arrow), respectively. Low-density nodules were observed in the corresponding CT images (C). Of the 3 lesions, the lesion in the thyroid isthmus was not found in ultrasound imaging. The abnormal foci (D) seen in the right neck and abdomen were the enlarged lymph nodes in the right neck and the hepatogastric space and the posterior of the pancreatic head. Based on the thyroid ultrasound results, thyroid cancer could not be excluded, and therefore the patient underwent thyroidectomy. Histopathologic examination after surgery showed non-necrotizing granulomas in the thyroid and neck lymph nodes and a negative acid-fast stain, leading to a morphologic diagnosis of tuberculosis. Thyroid tuberculosis is a rare disease, which often manifests as one or more space-occupying lesions in the thyroid lobes.^, The disease is diagnosed mainly by postoperative pathology, although it may be misdiagnosed as cancer before surgery.^, It has been reported that FAPI imaging agents are useful for identifying sites of tuberculosis.^–