Intrathyroidal paraganglioma is a highly uncommon entity, with fewer than 75 cases reported worldwide, and is typically discovered only after definitive histological evaluation following surgical excision. Its rarity and lack of distinctive clinical, radiological, or cytological markers mean that preoperative diagnosis is seldom suspected, often leading to unexpected findings at pathology. As in other head and neck sites, thyroid paragangliomas originate from parasympathetic paraganglia and rarely produce catecholamines, so most patients are asymptomatic except for an incidentally detected thyroid nodule. Nonetheless, perioperative screening for catecholamine excess remains prudent due to the low risk of hypertensive crises [1,2,3,4].

According to current guidelines for managing paragangliomas, biochemical screening for catecholamine excess should be limited to patients whose clinical presentation, genetic background, or imaging findings indicate a catecholamine-secreting tumor. Routine testing is not recommended as part of the standard diagnostic workup for thyroid nodules. In these selected cases, adrenal or extra-adrenal pheochromocytoma or paraganglioma must be rigorously excluded before any neck surgery. In this case, catecholamine assays were performed preoperatively because of the patient’s hypertensive symptoms, not due to suspected thyroid paraganglioma.

Diagnostic workup of suspicious thyroid nodules via ultrasonography and fine-needle aspiration (FNA) is typically inconclusive for paraganglioma, and the cytological features commonly overlap with those of other thyroid neoplasms such as follicular or medullary carcinoma. Only histopathology and immunohistochemistry can reliably establish the diagnosis, characterized by a nested (“zellballen”) arrangement of epithelioid cells, vascular stroma, and S‑100-positive sustentacular cells. Immunophenotypic confirmation requires positivity for neuroendocrine markers (such as synaptophysin, NSE, CD56) and the absence of thyroglobulin, TTF‑1, and calcitonin expression, distinguishing TPGL from major mimickers [1, 2].

From an ultrasonographic perspective, thyroid paraganglioma does not have pathognomonic morphological characteristics. Current ultrasound-based risk stratification systems, such as EU-TIRADS, may identify features suggestive of malignancy but cannot reliably distinguish this rare entity from more common differentiated thyroid carcinomas or other intrathyroidal neoplasms.

In our institutional practice, the presence of highly suspicious sonographic features (EU-TIRADS 4–5) in the context of indeterminate cytology is a major factor in recommending diagnostic lobectomy after a shared decision-making process with the patient, rather than relying solely on repeated fine-needle aspiration biopsy (FNAB). In this case, cytological evaluation showed thyrocytes mainly arranged in microfollicular clusters with scattered oxyphilic cytoplasm, mild anisocytosis, moderate colloid content, and occasional hemosiderin-laden macrophages, consistent with an indeterminate (Bethesda III–IV) pattern. Although ultrasonographic follow-up could have been considered, given the overall sonographic and cytological findings, a diagnostic lobectomy was proposed and accepted.

Hereditary paraganglioma syndromes should be considered, especially in younger patients and those with a family history, multifocal disease, or syndromic features, given that up to 25% of paragangliomas show germline mutations, most commonly involving SDH genes. Targeted genetic counselling has management implications for both the patient and their family [10].

Surgical excision remains the definitive and usually curative treatment, with lobectomy adequate for localized lesions and total thyroidectomy reserved for extensive disease. Adjuvant therapies, such as radiotherapy, are rarely needed except in cases with residual or aggressive histology [3, 11].

According to our institutional protocol, intermittent intraoperative neural monitoring (IONM) has been routinely used in thyroid surgery since 2004, with continuous IONM implemented since 2011. Both modalities were used in the present case. In contrast, intraoperative frozen-section examination is generally limited to lymph node assessment and is not considered informative for characterizing indeterminate thyroid nodules, which require definitive diagnosis through permanent histopathological analysis and immunohistochemistry.

Inadvertent parathyroidectomy, as occurred in our patient, is a well-recognized complication of thyroid lobectomy, particularly when the parathyroid gland is closely adherent to the thyroid capsule and intraoperative parathyroid autofluorescence is not used. In this case, the inferior parathyroid gland, located adjacent to the basal portion of the thyroid nodule, was inadvertently removed, while the superior parathyroid gland was clearly identified and preserved. The contralateral parathyroid glands were not explored and thus remained intact, highlighting the importance of careful dissection and postoperative biochemical monitoring.

While prognosis is generally favorable, the unpredictable biological behavior of TPGL—with reported instances of late recurrence or metastasis—requires long-term clinical and radiological surveillance. In summary, TPGL must be included in the differential diagnosis of indeterminate thyroid nodules. Its recognition depends on meticulous pathological workup, and its management hinges on surgical resection, judicious follow-up, and consideration of genetic testing where indicated [12].

As follow-up protocols for thyroid paraganglioma are not yet standardized, postoperative surveillance in our practice focuses on two main aspects: (1) monitoring residual thyroid function through periodic biochemical assessment (TSH and related parameters) and (2) evaluating the neck region with targeted imaging, primarily high-resolution ultrasonography, supplemented by additional modalities as clinically indicated. Given the limited available data and the potential for late recurrence, a structured, long-term follow-up strategy is advisable. This should include periodic neck imaging, symptom-triggered advanced investigations (such as MRI or functional imaging), and genetic counselling, with the goal of identifying delayed recurrences and detecting hereditary syndromes early. Systematic collection of clinical data from reported cases is essential to define optimal surveillance intervals, modalities, and duration.