# A rare primary mediastinal mesenchymal tumor diagnosed by endobronchial ultrasound (EBUS)

## TL;DR

A rare mediastinal tumor was successfully diagnosed using endobronchial ultrasound after other methods failed.

## Contribution

Demonstrates the effectiveness of L-EBUS in diagnosing rare mesenchymal tumors when conventional methods are inconclusive.

## Key findings

- L-EBUS provided a diagnostic tissue sample for a rare mediastinal mesenchymal tumor.
- The tumor was undifferentiated and showed high Ki-67 proliferation index.
- Multidisciplinary evaluation was essential for accurate diagnosis and treatment planning.

## Abstract

Primary mesenchymal tumors of the mediastinum are extremely rare and often pose considerable diagnostic challenges owing to their histological diversity and anatomical location. We report the case of a 51-year-old man with a 45 pack-year smoking history who was referred for evaluation of a mediastinal mass initially detected by chest radiography. Thoracic computed tomography (CT) and positron emission tomography-CT revealed a 3 × 3 cm lesion extending from the right upper and lower paratracheal regions into the right upper lobe parenchyma, demonstrating intense FDG uptake. Fiber-optic bronchoscopy revealed no endobronchial lesions. A CT-guided transthoracic needle biopsy was non-diagnostic. Subsequently, linear endobronchial ultrasound (L-EBUS) was performed, and a transbronchial needle biopsy sample was obtained for histopathological examination. Histopathological examination revealed an undifferentiated malignant mesenchymal tumor, positive for vimentin, with a Ki-67 proliferation index of approximately 30%. Despite an extensive immunohistochemical panel, no specific line of differentiation was established. Following the diagnosis, the patient was discussed at a multidisciplinary tumor board and subsequently referred to medical oncology for systemic treatment. This case highlights the role of L-EBUS in obtaining adequate tissue for the diagnosis of a rare malignant mesenchymal mediastinal tumor, particularly after inconclusive conventional biopsy attempts. Accurate diagnosis of such rare tumors requires a multidisciplinary strategy incorporating imaging, histopathology, and immunohistochemistry to guide appropriate treatment planning and prognostication of the disease.