CMR at 3T: Chasing Clues in a Right Atrial mass, Where Arrhythmia Darkens the Plot

Grigorios Melas MD, Isabelle Cardoso MD, Lousie McGrath BSc, Izgi Cemil MD

Royal Brompton and Harefield Hospitals, Guy’s and St Thomas’ NHS Foundation Trust, London, United Kingdom

Clinical History:

A 71-year-old female with a history of diabetes mellitus, hypertension, retinitis pigmentosa, and a possible past myocardial infarction associated with oral contraceptive use during her youth, was diagnosed with high-grade endometrial cancer. Preoperative staging identified a right atrial mass, which exhibited no increased metabolic activity on positron emission tomography (PET) scan (Figure 1).

Figure 1. PET scan axial plane. No increased metabolic activity on PET scan of the right atrial mass.

Echocardiography (Movie 1) revealed a large, heterogeneously structured soft tissue mass within the right atrium, featuring areas suggestive of calcification. No masses were observed originating from the inferior vena cava, and the right ventricular chambers were dilated with preserved right ventricular function.

Movie 1. Transthoracic echocardiogram contrast enhanced four chamber view. Large heterogeneous mass in the right atrium.

CMR Findings:

A CMR was performed at 3T (Siemens Magnetom Vida) adopting a mass protocol. A ECG- gated steady-state free procession (SSFP) sequence was then used to achieve the functional imaging in addition to localisation of the mass. The patient was in atrial
fibrillation with a heart rate of around 100 to 130 bpm and had poor breath hold capabilities. Therefore, real time adaptative triggering sequence was utilised to acquire the short axis, atrial and right ventricular trans-axial stack. The mass was
intricately connected to the fossa ovalis and exhibited dynamic movement in and out of the right ventricular cavity via the tricuspid valve during the cardiac cycle (Movie 2 and Figure 2). There was no gross invasion of the inferior vena cava or the superior vena cava.

Movie 2. Axial gated SSFP cine. The right atrial mass is seen entering into the right ventricle during the cardiac cycle.

Figure 2. Gated SSFP four chamber view at end-systole. Right atrial mass attached to the fossa ovalis.

T1-weighted double inversion recovery (DIR) fast spin echo (FSE) with and without fat saturation is part of the protocol but difficult to acquire due to poor ECG tracing in the setting of atrial fibrillation. Native T1 and T2 mapping in the 4 chamber, short axis and right ventricle in/outflow were imaged. The mass demonstrated iso-intensity to myocardium on T1-weighted images (Figure 3), contrasting with hyper-intensity on T2-weighted short tau inversion recovery (STIR) images (Figure 4).

Figure 3. T1 DIR FSE 4 chamber view. The right atrial mass is isointense in appearance.

Figure 4. T2 STIR four chamber view. The right atrial mass appears hyper-intense.

Similarly, the T1 relaxation time exhibited a slight increase (approximately 1380 ms at 3 Tesla, with a normal range of 1211-1333 ms, Figure 5), and there was an elevated T2 relaxation time value (49 ms, normal range 37-44 ms, Figure 6). STIR imaging was performed to assess for myocardial oedema. Trigger pulse 3, shortened TR and increased averaging making it a free breathing sequence were employed to improve image quality.

Figure 5. T1 map four chamber view. The right atrial mass T1 relaxation time is 1380ms (at 3 Tesla, normal range 1211-1333ms).

Figure 6. T2 map four chamber view. The right atrial mass T2 relaxation time is 49ms (at 3 Tesla, normal range 37-44ms).

Dynamic fast low angle shot (FLASH) imaging was used to assess the first-pass perfusion of the mass by a gadolinium bolus (Movie 3 and Figure 7). First pass perfusion in the planes identified for mapping was dynamically acquired using 0.1mmol/kg gadobutrol IV (Gadovist, Bayer Radiology, Leverkusen, Germany).

Movie 3 and Figure 7. First pass perfusion in 4 chamber view. There is no contrast enhancement of the right atrial mass.

Early gadolinium enhancement (EGE)(Figure 8) imaging was performed within 3 minutes of gadolinium injection using free breathing motion corrected phase sensitive inversion recovery (PSIR) sequence. An inversion time of 440ms was used
and trigger pulse 3 was selected due to the high heart rate.

Figure 8. EGE four chamber view. The right atrial mass is hypo-intense.

Late gadolinium enhancement (LGE) was performed 10 minutes post contrast injection (Figure 9). A fast gradient echo inversion recovery (IR-fast spin-echo) and free breathing motion corrected PSIR sequence was used. LGE imaging was acquired
in the short axis covering all the ventricles and in the optimal imaging planes mentioned above for tissue characterization of the mass. The mass remained hypo-intense of LGE sequences.

Figure 9. PSIR four chamber view. The right atrial mass is hypo-intense on this LGE sequence.

Overall CMR findings were suggestive of a thrombus. While the mass’s features were indicative of a thrombus, its location was unusual, and the potential presence of a myxoma with thrombus could not be ruled out, as the location was more in line with atypical myxoma presentation.

Conclusion:

The case was presented in the Cardio-Oncology multidisciplinary meeting, where it was agreed that given the mass’s substantial size and the associated risk of thromboembolism, the consensus decision was surgical resection. Coronary computed tomography (CT) angiography unveiled an isolated high-grade lesion proximal to the left anterior descending artery (LAD)(Figure 10). A Cardiac CT was also requested for better visualization of the mass (Figure 11). Consequently
the patient underwent a left internal mammary artery (LIMA) to LAD bypass graft procedure alongside the resection of the right atrial mass.

Figure 10. Maximum intensity projection coronary CT. Proximal LAD stenosis.

Figure 11. Chest CT with contrast axial projection. Right atrial mass present.

Macroscopically the mass had the appearance of a myxoma encased within organized thrombus. The post-operative transesophageal echocardiogram (TOE) revealed an entirely satisfactory outcome, showcasing successful tricuspid valve repair with mild residual tricuspid regurgitation and the complete excision of the right atrial mass. In histology, the immunohistochemical profile confirmed a diagnosis of myxoma with degenerative changes.

Perspective:

The goals of the CMR sequences selected are to define the extent and nature of the mass by its T1, T2, and T2* effects to use cine sequences to identify mobility of the mass to determine compromise of valvular function and to determine enhancement pattern of the mass and invasion of the mass into coronary vasculature [1]. The modern multi-modality imaging techniques have a key role not only for the primary assessment and differential diagnosis but also for management and surveillance of the cardiac masses [2]. CMR is the most important modality in differentiating tumour from thrombus, distinguishing benign from malignant cardiac masses, and to determine the extent of myocardial and pericardial invasion in cardiac masses [3]. However, histological examination still remains the gold standard [4][5]. The frequency of endometrial cancer is 25.7/100000 and although cardiac myxoma are the most common primary heart tumours, accounting for 40-50% of primary cardiac tumours, the risk of developing an atrial myxoma is approximately 0.02%. The reported incidence of endometrial cancer and a concurrent atrial myxoma are very rare.

This case highlights the importance and challenges of CMR in characterization of cardiac masses. In assessing cardiac mass, the protocol must be tailored in terms of the optimal acquisition planes and sequences in order to obtain localisation and
accurate tissue characterisation. In this instance, there were several challenges from the offset, primarily related to the suboptimal ECG and the extensive image artefacts, related to a high magnetic field strength (3 Tesla). Improving CMR in the setting of arrhythmia presents several challenges due to the motion artifacts caused by irregular heartbeats. However, there are techniques and strategies that can help mitigate these challenges and enhance the quality of CMR in patients with
arrhythmia. The following are techniques and solutions to improve CMR in the setting of arrhythmia: 1: use of b-blockers or other antiarrhythmic drugs before the scan to regulate patient heart rate, 2: increase breath holding time, 3: respiratory
gating techniques to minimize breathing-related motion artifacts that can be particularly important in atrial fibrillation patients who may have difficulty holding their breath consistently, 4: prospective triggering, and 5: real-time imaging allows
for the acquisition of images over multiple cardiac cycles that can help in capturing images during different phases of the cardiac cycle, minimizing the impact of arrhythmias on image quality.

In this case, the patient was a poor breath holder, she was not on any b-blockers or other antiarrhythmic drug and the physiological ECG/ respiratory unit PERU098 (Siemens Healthineeers, Erlangen, Germany) was not available for use on the day. Real time adaptative triggering sequence was utilised to acquire the short axis, atrial and right ventricular trans-axial stack. This sequence has reduced temporal resolution, spatial resolution, and signal to noise ration (SNR) but was superior in image quality to the cine SSFP images acquired.

Thrombi and cardiac masses have different imaging characteristics on CMR. Thrombi typically appear as hypointense on long TI sequences due to their lack of perfusion and oxygenation, while other masses such as tumours or fibrosis are isointense, hyperintense, or heterogenous. Long TI sequences (600 ms at 1.5 T, 800 ms at 3 T) can help in characterizing the composition of the tissue by highlighting differences in signal intensity based on tissue properties such as T1 relaxation times. Thrombi and masses may have distinct T1 relaxation times, aiding in differentiation.

In summary, long inversion time sequences in CMR play a valuable role in differentiating thrombus from other cardiac masses by providing detailed tissue characterization. However, some myxomas may be mistaken for thrombus in case of absence of a visible vascularized stalk and gelatinous appearance [5]. In the following Table 1, we present what is expected to find in a myxoma case and the findings in our study [2].

	T1	T2	EGE	LGE	T1map	T2map
Myxoma expected findings	Isointense	High	Heterogenous	Heterogenous	High	High
Our findings	Isointense	High	No enhancement	No enhancement	High	High

Table 1: The comparison of the expected findings vs findings in our case [6]

Furthermore, while CMR is an optimal non-invasive method for localizing cardiac lesions, offering valuable multiplanar information and tissue characterization, the interpretation of these findings should always consider the clinical context [7]. Although the location of the cardiac mass is crucial in the differential diagnosis, it should always be in consideration with the patient clinical status and comorbidities [8,9].

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References:

Case prepared by:

Anna Baritussio, MD, PhD
Editorial Team, Cases of SCMR
Department of Cardiac, Thoracic, Vascular Sciences and Public Health, University Hospital Padua, Padua, Italy