Thinking outside the box: an unusual case of a pericardial mass.

Description of Clinical Presentation: A 57-year-old man with no medical history presented with presyncope, dyspnoea, and chest tightness after recent travel to Nepal via Doha, with no asbestos exposure. Electrocardiography on admission demonstrated low-amplitude QRS complexes without significant ST-segment changes. A focused bedside ultrasound revealed a large pericardial effusion with echocardiographic features consistent with cardiac tamponade. Pericardiocentesis was performed within 24 hours of admission, yielding 850 mL of haemorrhagic fluid, and markedly improving the right ventricular function and haemodynamic stability. Computed tomography coronary angiography (CTCA) performed the same day demonstrated a centrally hypodense mass measuring 77 × 59 mm, located between the pericardium and the right cardiac chambers. The lesion showed an incomplete rim of peripheral calcification (Figure 1), suggesting a possible mediastinal teratoma.

Diagnostic Techniques and Their Most Important Findings: A comprehensive CMR tumour protocol including T1/T2 weighted, STIR short tau inversion recovery, T1/T2 mapping, real-time deep breathing cine and early and late gadolinium enhancement sequences was performed to better characterise the pericardial mass.

The CMR images revealed an encapsulated, inhomogeneous signal mass (81 × 59 × 42 mm) in the right ventricular groove, anterior to the aorta, without myocardial infiltration. The right coronary artery was displaced inferiorly but remained patent. Tissue characterisation showed a septated cystic lesion with fluid content and an inflamed capsule (figure 2). Mild pericardial thickening and inflammation were noted. While the lesion cavity showed no contrast uptake, both the capsule and pericardium enhanced post-gadolinium injection. Mild RVOT compression and septal flattening on real-time imaging were consistent with mild constrictive physiology. The CMR characteristics were not clearly in favour of malignancy and therefore, the differential diagnoses included pericardial tuberculosis or a hydatid cyst.

Due to recurrent tamponade and haemodynamic instability, the patient underwent urgent on-pump pericardiectomy one month after presentation, including cyst deroofing, RCA decompression, and IVC repair. Histopathology confirmed poorly differentiated malignant pericardial mesothelioma. Given the advanced stage and poor prognosis, no further treatment was offered following multidisciplinary review. The patient died 50 days after initial admission.

Learning Points from this Case: This case raises awareness of primary pericardial mesothelioma—an exceptionally rare, aggressive malignancy with non-specific symptoms and variable imaging features (table 1).

Primary pericardial mesothelioma is an exceptionally rare malignancy, with a reported incidence of 0.0022% and up to 75% diagnosed post-mortem. Antemortem diagnosis is challenging due to its varied presentation and non-specific imaging. In this case, these factors delayed diagnosis until histopathological confirmation on day 30 of admission.

Table 1. Common characteristics of primary pericardial mesothelioma.

Signal Intensity-T1 weighted imaging-T2 weighted imaging-Late gadolinium enhancement (LGE)	isointense to the myocardiumheterogenous with elevated signal intensity (necrosis, haemorrhage)heterogenous enhancement indicating tumour viability and vascularity
Morphology-Pericardial Masses-Pericardial effusion-Tumour invasion	multiple ill-defined nodular masses causing extensive thickeninglarge haemorrhagic or exudative pericardial effusionnodular protrusions from pericardium suggest invasion
Haemodynamic impact-Constrictive pericarditis-Cardiac tamponade-Cardiac deformation	diffuse pericardial involvement causing constrictive physiologymassive pericardial effusion potentially causing tamponadecompression of atria and ventricles leading to deformation

Figure 1. Computer tomography coronary angiography: Mediastinal (A) and lung (B) windows showing the pericardial mass (hypointense mass with peripheral calcifications).
Figure 2. Tissue characterisation of the tumour. A. Cine SSFP (T2/T1 weighted image). B. T1-weighted sequence. C. T2-weighted sequence. D. STIR sequence. E. Native T1 map. F. T2 map. G. Early Gadolinium enhancement. H/I. Late Gadolinium enhancement (Magnetisation/PSIR).