Invasive thymoma - invading the superior vena cava and right atrium

Clinical History

A 57-year-old man came with puffiness of the face and upper limbs, cough with minimal expectoration and progressive shortness of breath with dull chest pain for the past 2-3 months with weight loss and anorexia. The patient was a chronic smoker. Routine investigations were normal, so a contrast-enhanced chest CT was advised.

Imaging Findings

A contrast-enhanced CT thorax revealed an abnormal well-defined lobulated, hypodense, mildly enhancing soft tissue lesion with multiple calcifications within the prevascular space of the anterior mediastinum. There was no evidence of necrosis, cystic areas or variable attenuation ruling out mediastinal germ cell tumours. In the retrosternal area, the lesion was abutting the posterior aspect of the sternum. Multiple collaterals were noted in the right axilla, around the scapula and also in the anterior chest wall (Fig. 2). The lesion was encasing the superior vena cava and the origin of the right brachiocephalic trunk (Fig. 3, 4). It was invading the pericardium and was extending into the right atrium forming an intraatrial polypoidal lesion projecting into the lumen - a very classical finding of invasive thymoma (Fig. 5, 6, 7]. A CT-guided biopsy was performed and histology confirmed the diagnosis of thymoma (Fig. 8).

Discussion

Thymic epithelial tumours are mostly located in the anterior mediastinum, although cases in the neck and posterior mediastinum have been reported.
Age of onset is usually 40-60 years. No sex predilection is noted.
Clinically, they can present with chest pain, cough, venous obstruction, dysphagia or stridor. Associated conditions are myasthenia gravis, pure red cell aplasia, hypogammaglobulinaemia, systemic lupus erythematosus (SLE), rheumatoid arthritis, etc.
Thymic tumours are classified into non-invasive thymoma and invasive thymoma and carcinoma (Fig. 1). According to Masoka's classification, our patient had Stage III thymoma and WHO classification C. Macroscopically thymic tumours are of variable shape, with thymoma being typically rounded with a bosselated outer surface and lack of histologic evidence of malignancy [1].
CT imaging: One of the important—though challenging—roles of CT is to determine local tumour invasiveness. This is crucial, as tumour invasiveness has been shown to strongly correlate with prognosis and dictate the therapeutic approach.
Thorough MRI vascular involvement can be investigated without the use of intravenous contrast agents, however, the disadvantage of a lengthy procedure and poor investigation of the lung parenchyma outweighs its rationale in comparison to computed tomography.
Thus, if the aetiology of the anterior mediastinal mass is not known, a complete investigation of it by MRI is not optimal and CECT is preferred as it covers the evaluation of the lung parenchyma [2].
Studies assessing the evaluation of thymoma with FDG-PET modality are small, but the data is not promising. Although FDG uptake was found to be much higher in thymic cancer than thymoma, the amount of uptake, or as it is termed standardized uptake value (SUV), overlaps between low-grade and high-grade thymomas.
Treatment depends on the stage as well as the presence of myasthenia gravis, which mandates earlier surgical excision. For thymoma, local excision usually suffices and complete excision results in cure. For invasive thymoma, surgery may still be contemplated if complete excision is thought possible. If not, then down-staging with preoperative chemotherapy may be employed. Radiotherapy is not usually employed for stage I thymoma, but has a role in both post-surgical management of resected invasive thymoma or for inoperable invasive tumours, including thymic carcinoma. Our patient was advised chemotherapy to downsize the tumour, after which tumour resection was performed with cardiopulmonary bypass.

Differential Diagnosis List

Final Diagnosis

Grade III invasive thymoma

URL:	https://www.eurorad.org/case/12282
DOI:	10.1594/EURORAD/CASE.12282
ISSN:	1563-4086