# Microscopic thymoma with a thymic cyst that enlarged over a 2-year period

## TL;DR

A patient with lung cancer had a small mediastinal nodule that grew over two years and was found to be a microscopic thymoma near a thymic cyst.

## Contribution

Demonstrates that microscopic thymoma can occur near thymic cysts without myasthenia gravis and should be resected.

## Key findings

- A 6 mm mediastinal nodule grew to 13 mm over two years.
- Pathological examination revealed a 400 μm microscopic thymoma near a thymic cyst.
- Surgical resection via a robotic approach was effective and safe.

## Abstract

An 81-year-old woman was referred to our hospital because of right lung cancer. She underwent right upper lobectomy. Pathological examination revealed stage 1A adenocarcinoma. Four months postoperatively, chest computed tomography showed a small nodule with a diameter of 6 mm at the anterior mediastinum. After 2 years, the nodule had increased to 13 mm. To confirm the diagnosis and treat the mediastinal tumor, we resected the tumor and surrounding thymic tissue by a left robotic thoracic approach, considering the adhesion in the right thoracic cavity after right pulmonary resection. The operating time was 43 min. The patient had a favorable postoperative course and was discharged 3 days after surgery. Pathological examination revealed microscopic thymoma with a diameter of 400 μm very close to a thymic cyst. Microscopic thymoma can occur around a thymic cyst without myasthenia gravis, and the thymic tissue around the anterior mediastinal cyst should be resected.