# Expanding the Phenotypic Spectrum of Differentiated High-Grade Thyroid Carcinoma: An Extracranial Mass as the First Presentation

## TL;DR

A rare thyroid cancer case presented as an extracranial mass, highlighting challenges in diagnosing and managing this newly classified tumor.

## Contribution

This case expands the known presentation of differentiated high-grade thyroid carcinoma (DHGTC) as an extracranial mass.

## Key findings

- DHGTC presented as a cranial mass with metastatic features in a 52-year-old male.
- Histopathology confirmed DHGTC with papillary features and tall cell morphology.
- The case emphasizes the need for early diagnosis and multidisciplinary management of DHGTC.

## Abstract

Differentiated high-grade thyroid carcinoma (DHGTC) is a recently recognized entity introduced in the 2022 World Health Organization (WHO) Classification of Endocrine and Neuroendocrine Tumors. The prognosis is intermediate between differentiated thyroid carcinoma, which generally has a favorable outcome, and anaplastic thyroid carcinoma, which carries a poor prognosis. Given its recent classification, standardized management guidelines and long-term follow-up data are lacking.

We report a case of a 52-year-old male who presented with a protruding cranial mass with overlying wound dehiscence. Initial pathological analysis of the mass revealed metastatic thyroid carcinoma. Further workup identified a 7 cm × 5 cm mass at the right vertex, invading the right parietal bone and extending into the epidural space. Additionally, a large thyroid mass was observed, causing destruction of the manubrium sternum and upper ribs, with subcutaneous and superior mediastinal extension. The patient underwent cranial mass resection and biopsy of the superior mediastinal mass. Histopathological examination confirmed DHGTC with papillary features and tall cell morphology, involving the dura mater, parietal bone, and scalp. The superior mediastinal biopsy also demonstrated high-grade thyroid carcinoma. The patient had a history of autism spectrum disorder with nonverbal communication. Given the advanced disease stage, the family opted for comfort care.

This case highlights the new histopathological criteria for DHGTC and its unusual presentation, emphasizing the challenges in management and prognosis of this newly defined entity. Clinicians should consider DHGTC in atypical extracranial metastatic presentations to facilitate early diagnosis and multidisciplinary management.