Unusual thoracic presentation: The case of a 17 cm pleural mass

A 73-year-old female, a lifelong non-smoker with a previous medical history of hypothyroidism and osteoporosis, was referred to the pulmonology outpatient clinic due to complaints of dyspnoea (mMRC grade 2), orthopnoea, asthenia, and 22% weight loss over the past three months. Physical exam showed no respiratory distress, 97% oxygen saturation, and asymmetric breath sounds with diminished right hemithorax sounds.

Chest x-ray (Figure 1) showed a pulmonary opacity in the right hemithorax causing contralateral deviation of the trachea without other abnormalities. A thoracic contrast CT scan was ordered for better characterisation of the lesion (Figures 2a, 2b and 2c), which revealed, in the right hemithorax, a globular pleural-based mass measuring 172x120x100mm with scattered areas of lower density. No mediastinal lymphadenopathy or other significant abnormalities were noted. A dual-phase 18F-FDG PET-CT scan (figures 3a and 3b) showed hypermetabolic activity in this lesion (SUVmax: 5.8), excluding other sites of abnormal FDG uptake.

The patient’s age, symptoms, and clinical course suggested a potential diagnosis of lung cancer. Initial evaluation with x-ray revealed a significant opacification in the right hemithorax, and the CT scan confirmed the presence of a large pleural-based mass. When faced with a large pleural mass, one of the possible diagnoses is a solitary fibrous tumour (SFT) of the pleura. Despite rare, a malignant nature cannot be ruled out, and tru-cut biopsy is associated with a non-negligible potential for seeding, discouraging this approach [1]. However, the homogeneous CT scan appearance was non-expected in a SFT, prompting the lung cancer multidisciplinary team to assess further using an echo-guided fine-needle biopsy.

The biopsy revealed an abundant population of lymphocytes with immature T-cells and occasional epithelial cells (Cam 5.2+/p63+). Markers were positive for CD2, CD3, CD5 and TdT, findings consistent with type B1 thymoma.

Putting aside the main initial diagnostic suspicions, the anatomopathological evaluation led to the diagnosis of an ectopic type B1 thymoma located in the pleura. This is a rare presentation of this neoplasm which typically appears as a mediastinal mass.

A thymoma is a rare tumour usually located in the anterior thymus. Few cases have been described of this tumour’s presence in other locations, such as the neck, thyroid, pleura, and pericardium [2]. When present as a thoracic mass, it typically appears, as in this case, with large dimensions [3–5].

The clinical case was discussed in a lung cancer multi-disciplinary meeting, during which a total surgical resection of the malignancy was decided. The surgery proceeded without complications, and cancer-free margins were obtained in the pathological evaluation of the surgical specimen, both associated with good long-term prognosis.

This is a rare presentation of a type B1 thymoma, highlighting the importance of combining imaging, histological, and immunohistochemical evaluations in establishing the diagnosis of a thoracic mass and recognising the existence of atypical presentations.

All patient data have been completely anonymised throughout the entire manuscript and related files.