Central hyperthyroidism due to an ectopic TSH-secreting pituitary tumor: a case report and literature review

Abstract

Ectopic thyroid-stimulating hormone (TSH)-secreting tumors are extremely rare, with only 15 reported cases in the literature. Herein, we described a 60-year-old female patient with thyrotoxicosis and elevated or unsuppressed levels of TSH. Family history and laboratory and genetic tests did not support a diagnosis of resistance to thyroid hormone (RTH). Given the unsuppressed TSH, TSH-secreting tumor was suspected, and magnetic resonance imaging (MRI) of the pituitary gland was performed. Surprisingly, the MRI scans revealed a nodule in the nasopharynx rather than a pituitary tumor in the sella region. Further evaluation using Gallium-68 DOTATATE positron emission tomography/computed tomography (⁶⁸Ga-DOTATATE PET/CT) demonstrated increased DOTATATE uptake in the nasopharyngeal nodule. Additionally, an octreotide suppression test (OST) revealed an obvious reduction in TSH levels, further supporting the suspicion of the nasopharyngeal mass as the cause of inappropriate TSH secretion. To prepare for surgery, the patient received preoperative administration of octreotide, resulting in the normalization of TSH and thyroid hormone levels. The patient subsequently underwent successful surgical removal of the nasopharyngeal mass. Following the procedure, the patient experienced complete resolution of hyperthyroidism symptoms, with TSH declined and thyroid hormone levels returned to normal. Histochemistry analysis of the tumor revealed positive staining for TSH, growth hormone (GH), prolactin (PRL), luteinizing hormone (LH), and somatostatin receptor 2 (SSTR2). We discussed differential diagnosis of hyperthyroidism due to inappropriate TSH secretion, with a particular emphasis on the importance of ⁶⁸Ga-DOTATATE PET/CT in combination with OST for identifying ectopic pituitary tumors.

Keywords: 68 Ga-DOTATATE PET/CT; TSH-secreting tumor; diagnosis; ectopic pituitary tumor; octreotide suppression test.

Figure 1

Imaging of MRI and CT. T1-weighted sagittal (A) and coronal (B) magnetic resonance imaging reveal a mildly enhancing nasopharyngeal nodule (red arrow) and normal pituitary (yellow arrow). Computed tomography (C) shows a nasopharyngeal soft tissue nodule.

Figure 2

Imaging of ⁶⁸Ga-DOTATATE PET/CT and ¹⁸F-FDG PET/CT. There is a soft tissue nodule at the apex of the nasopharynx with ⁶⁸Ga-DOTATATE (A) and ¹⁸F-FDG (B) intense uptake.

Figure 3

Pathological and immunohistochemical staining results of tumors. Under the microscope, the tumor is composed of sheets of uniform small cells with slightly eosinophilic cytoplasm and round to oval nuclei (hematoxylin and eosin, ×400). Some tumor cells arrange in a pseudorosette pattern (A). Immunohistochemistry stain (×400) demonstrates diffuse and strong reactivities against both TSH (B) and SSTR2 (C).