MRI for the diagnosis of cardiac tumors

Epidemiology

Primitive tumors of the heart and of the pericardium are very rare. Of these, approximately 75% are benign and 25% are malignant. In adults the most common benign tumor is the mixoma, in children the rhabdomyoma (40%), and in infants the rhabdomyoma and the theratoma. Of the malignant tumors -more common in adults than in children- 33% are angiosarcomas, 24% rhabdomyosarcomas, 15% mesotheliomias and 10% are fibrosarcomas.

Diagnostic strategy through MRI

The introduction of MRI in the study of the cardio-vascular apparatus has notably modified the diagnostic strategy of intra-cardiac masses (1-2). Once intracardiac mass is suspected in patients following an echocardiographic study, they are often referred for an MRI  evaluation.

This technique provides a complete multiplanar and non-invasive evaluation of the lesions involving the cardiac chambers, pericardium and extracardiac structures, assuming a relevant role in providing diagnostic information useful toward surgical planning. The details to assess are: morphology, dimensions, location, extension, topographic relation, presence of infiltration in the surrounding tissues, and the signal characteristics that can help for a histopatologic characterisation (presence of adipose tissue, necrosis, hemorrhage, calcification, mixoid tissue, vascularisation, etc). In reality, the histopatologic characterisation of lesions is rarely possible except for lipomatose forms (subtraction or suppression of fat). Often, the diagnosis is based on indirect and probabilistic findings, which orientate towards a kind of tumor rather than another.

How MRI works

A correct characterisation of the cardiac and paracardiac mass requires integrated information that is obtainable with the different MRI sequences available. In other words, to characterise a cardiac mass, it is necessary to obtain images in T1, T2,  Inversion Recovery or, T1/T2 with spectral suppression of the fat, Gradient Echo T2* (star) (for eventual calcifications or hemorrhages on the inside of the mass), in T1 after paramagnetic contrast medium. Furthermore, it is suggested to obtain images in cine for the study of the movement of the wall involved.

These are generally quite lengthy studies (one hour) which often may bring the physician very close to the nature of the tumor. Table 1 reports the characteristic signals of the various tissue components useful for a diagnostic orientation.

Table I
Characteristics of the MRI signal from varied tissues in the T1- e T2-weighed images.

* The type of signal and capture depends on the vascularisation and the cellularity of such tissues (modified by MRI of the Heart and Vessel – M. Lombardi and C. Bartolozzi Eds. 2005, Springer – Verlag – Milan, Berlin)

Diagnostic Accuracy

Hoffmann et Al. (3) have evaluated a cohort of more than 200 cardiac masses and evaluated their signal properties and morphologic characteristics (location, dimension, homogeneity, infiltrative nature, presence of pericardial or pleural effusion, dislocation of surrounding structures) and enhancement of the signal after contrast agent administration. It is noteworthy that no single variable is 100% accurate. On the other hand, in the vast majority of cases, the integration of the above mentioned information allows to reach a highly probable diagnosis. The quality of images, the large view field and the spontaneous contrast between different tissues and different components of the same tissue make MRI the ideal tool in such a pathology. It should be used for the reoperative evaluation and follow-up of patients with a cardiac tumor.

Conclusion

Echocardiography remains the first diagnostic approach when suspecting a cardiac tumor that often appears unexpectedly during an echocardiographic examination. Yet MRI offers several adjunctive advantages which make this technology the most sophisticated among the imaging techniques available today. As the number of centers offering this advanced application of MRI is rapidly growing worldwide, a reasonable and realistic imaging approach should be to conjugate Echocardiography and MRI in the diagnostic process and during follow-up.

Table  II
Diagnostic accuracy of morphologic characteristics and enhancement after contrast agent administration (PPV=positive predictive value); (NPV=negative predictive value).

Modified from Hoffmann et al. (Am J Cardiol 2003;92:890-895)

Legend of Figure 1
A case of undifferentiated sarcoma. Left panel: presence of a mass infiltrating and expanding within the left atrium (arrows). Right panel: after contrast agent administration it is evident the enhancement of the signal within the tumoral mass (arrows).