# Collision thyroid tumors: a case report of coexisting papillary and follicular carcinoma

## TL;DR

A rare case of a thyroid tumor containing both papillary and follicular carcinoma is reported in a 73-year-old woman.

## Contribution

This case adds to the limited literature on collision thyroid tumors involving papillary and follicular carcinoma.

## Key findings

- The patient had a thyroid nodule classified as Bethesda IV via fine-needle aspiration.
- Histopathology confirmed coexisting papillary and minimally invasive follicular carcinoma.
- The tumors were anatomically distinct and separated by normal thyroid tissue.

## Abstract

Collision tumors of the thyroid gland are defined by the coexistence of two or more histologically and morphologically distinct neoplasms, separated by normal thyroid tissue. This phenomenon is rare, with the most frequently reported combination being the coexistence of medullary carcinoma and papillary carcinoma. This case reports a 73-year-old female patient with an asymptomatic thyroid nodule. Ultrasonographic examination revealed a solid, isoechoic, well-defined nodule with a halo and peripheral vascularization, measuring 4.3 × 2.5 cm in the left lobe. Fine-needle aspiration cytology classified the nodule as Bethesda IV (follicular tumor). Following total thyroidectomy, histopathological analysis identified papillary carcinoma in the isthmus and minimally invasive follicular carcinoma in the left lobe.