MRI PROTOCOL
- Pre- and post-contrast T1-weighted black blood images.
- T2-weigthed turbo (fast) spin echo imaging before and after fat suppression.
- Electrocardiography (ECG)-gated cine steady state free precession (SSFP) imaging in 2 chambers,
4 chambers and short-axis orientation,
or in any other oblique plane depending on the location of the tumor.
- Myocardial delayed enhancement imaging with IR sequences.
- 3D gradient echo bright blood sequence with diaphragmatic navigator and prospective slice correction.
- Proton density black blood images.
BENIGN TUMORS
Myxoma (Case 1,
2)
Myxoma is the most common primary cardiac neoplasm in adults (1,5).
The most common location of myxoma is the left atrium and typically it arises near the fossa ovalis the interatrial septum (2,5).
Myxoma is highly mobile and occasionally protrudes into the respectively atrioventricular valve during causing obstruction (2,6).
Areas of hemorrhage,
fibrosis,
and foci calcification are frequently inentifies in the tumor (5,6).
At MR imaging,
the vast majority of myxomas have heterogenous signal intensity reflecting the underlying heterogeneity of the tissue.
Myxomatous tissue has low signal intensity relative to myocardium on T1-weighted images and high signal intensity on T2-weighted images; fibrous tissue and foci of calcifications are hypointense on both T1- and T2-weighted images,
while areas of hemorrhage show variable signal intensity depending on the stage of blood products (2,3,5,6).
Enhancement following administration of gadolinium contrast material is usually heterogenous,
although occasionally enhancement is homogenous (5,7).
Cine images are useful for the assessment of the lesion mobility (with or without prolapse through the respectively atrioventricular valve) and attachement (although the site of the attachment to the interatrial septum may not be seen,
especially for tumors with short stalk) (5,8).
Fibroelastoma
Fibroelastoma is a benign endocardial papilloma (typically small in size) that can arise from any endocardial surface,
but the vast majority (90%) affects the cardiac valves with a slight predilection for the left-sided valves (6,8).
At MR imaging,
fibroelastoma typically appears as a well-defined small homogenous valvular mass,
which is better assessed with cine images showing a highly mobile hypointense lesion with surrounding turbulence of blood flow (2,8).
Lipoma (Case 3)
Lipoma is a homogenous encapsulated neoplasm consisted of adipose cells (4,8).
It may arise from the epicardial surface with extension into the pericardial space or from the endocardium or myocardium protruding into the adjacent cardiac chamber with broad base of attachment (5,8).
Lipoma is easily diagnosed with CMR.
The key MRI finding is homogenous high signal intensity on both T1- and T2-weighted images similar to that of adjacent subcutaneous or mediastinal fat with characteristic signal loss using fat saturation techniques (5,
9,10).
Lipomatous hypertrophy (Case 4) of the interatrial septum is another fat-containing lesion in the heart.
Lipomatous hypertrophy is a benign condition (not a true) that results from non-encapsulated adipose cell hyperplasia in the atrial septum with a diameter greater than 2cm (4,8).
It characteristically spares the fossa ovalis giving a dumbbell shape in the lesion (4,6).
Rhabdomyoma
Rhabdomyoma is the most common primary cardiac neoplasm in the paediatric population and rarely will be found in early adulthood (1,11).
It originates within the myocardium and is commonly located within the ventricles.
Rhabdomyoma is usually multiple and is associated with tuberous sclerosis (3,
11).
At MR imaging,
rhabdomyoma is homogenous on all sequences and appears isointense to myocardium on T1-weighted images and hyperintense on T2-weighted images (6,11,12).
It shows typically show minimal or no enhancement with gadoliniumand may remain hypointense after contrast administration (3,5,6).
Fibroma (Case 5)
Fibroma is primarily present in infants and children and have rare association with polyposis syndromes (2,6).
Cardiac fibroma typically has intramyocardial location and affects the ventricles,
mainly involving the interventricular septum (11,
12).
Those associated with polyposis syndromes appear more often in the atria (2,6).
Calcification within the center of the mass is a common feature (3,11).
The fibrous nature of the tumor produces homogeneously hypointense signal on T2-weighted images (2,3).
Although calcification is difficult to distinguish on MRI,
it may be seen as central low signal foci.
Little or no tumoral enhancement is usually seen on perfusion images,
while hyperenhancement on late gadolinium-enhanced images with or without a hypoenhancing (dark) core due to the presence of calcium is often reported (6,11,12).
Hemangioma (Case 6)
Hemangioma is benign vascular tumors that can be found at any age can be located in any chamber of the heart (3,5).
At MR imaging,
hemangioma is isointense or hypointense on T1-weighted images and typically hyperintense on T2-weighted images (3,5).
Strong enhancement is observed during and after contrast administration due to the rich vascularity of the tumor (6,11).
MALIGNANT TUMORS
Primary malignant tumors of the heart are predominantly sarcomas,
followed by primary cardiac lymphoma (6,8).
Secondary cardiac tumors are much more common.
Findings suggestive of malignancy at MR imaging are right side location,
involvement of more than one chamber of the heart,
pericardial involvement (disruption of fat planes,
pericardial thickening or nodularity,
hemorrhagic pericardial effusion),
large size (diameter greater than 5 cm),
and tissue inhomogeneity with heterogeneous post-contrast enhancement.
Invasive behavior with extension into the mediastinum or/and the great vessels is also a clear sign of malignancy.
(3,4,6,8)
Angiosarcoma
Angiosarcoma is the most common cardiac sarcoma in adults (2,3).
The tumor is highly aggressive with large areas of hemorrhage and necrosis and typically involves the right atrium (8).
CMR typically demonstrate a large right atrial mass with heterogeneous signal intensity on T1-weighted and T2-weighted images reflecting tumor tissue,
necrosis,
and areas of hemorrhage (3,6).
After contrast administration,
it shows heterogeneous strong enhancement.
Pericardial involvement may be seen (5,8).
Rhabdomyosarcoma
Rhabdomyosarcoma is the most common cardiac sarcoma in children (embryonal subtype),
however the much less frequent pleomorphic subtype occurs mainly in adults (3,8).
It arises from the myocardium with predilection for any specific cardiac chamber (although more often involves cardiac valves) and has a tendency to be multiple (11).
At MR imaging,
rhabdomyosarcoma is appears isointense to myocardium on T1-weighted images,
but areas of necrosis cause heterogeneous signal intensity and enhancement pattern (3,11).
Other sarcomas (Case 7)
Other possible primary cardiac sarcomas are undifferentiated sarcoma,
fibrosarcoma,
leiomyosarcoma,
liposarcoma,
and osteosarcoma.
These tumors are extremely rare and demonstrate nonspecific MRI features (6).
The majority of these entities are isointense to myocardium on T1-weighted images and hyperintense on T2-weighted images and show vary degrees of heterogeneous enhancing with gadolinium contrast material (3,6,8).
Liposarcoma rarely has macroscopic adipose tissue and does not resemble benign lipoma (2,8).
A finding in favour of osteosarcoma is the presence of calcification.
Because calcification is difficult to distinguish on MRI,
CT is recommended in all suspected cases of osteosarcoma.
(3,8)
Primary cardiac lymphoma
Primary cardiac lymphoma is extremely rare and most commonly occur in immunocompromised patients.
Almost all primary cardiac lymphomas are aggressive non-Hodgkin B-cell type (2,3).
It commonly affect the right side of the heart and may be multiple (6,11).
Pericardial invasion is often.
At MR imaging,
lymphoma typically appear homogeneous,
isointense on T1-weighted,
isointense to slightly hyperintense on T2-weighted images and demonstrates heterogeneous contrast enhancement (3,6,8).
Secondary tumors (Case 8)
Metastatic involvement of the heart is much more common than primary cardiac neoplasms (3,10).
Cardiac metastasis may occur via the lymphatic or hematogenous route or by direct or transvenous extension (2,
13).
Melanoma and lymphoma are the tumors that most frequently metastize to the heart.
Bronchial,
breast,
and esophageal tumors can invade the heart directly due to their proximity.
Renal cell carcinoma,
hepatoma,
and adrenal adenocarcinoma can extend through the inferior and carcinoma of the lung and thyroid gland through the superior vena cava into the right atrium.
At MR imaging,
most cardiac metastasis are of low signal intensity on T1-weighted images and high signal intensity on T2-weighted images without reflecting the organ of origin with the exception of melanoma which may appear high signal intensity on T1-weighted images owing to the paramagnetic effect of melanin (2,6,8).
Pericardial effusion is a common associated feature of metastatic involvement of the heart,
which is frequently hemorrhagic or exudative having high signal intensity on T1-weighted images (3,6).
TUMORLIKE LESIONS
Thrombus (Case 9)
Thrombus is the most common cardiac mass and frequently can mimic a cardiac tumor.
The signal intensity of thrombus vary at MR imaging depending on age-related changes and the intravenous administration of paramagnetic contrast agent enables a confident diagnosis (6,8).
Acute thrombus has high signal intensity on both T1- weighted and T2-weighted images,
whereas older thrombus shows low signal intensity on T1-weighted images (6,11).
Almost all tumors show enhancement on post contrast images,
while thrombus does not enhance (although chronic organized thrombus may show some peripheral enhancement) (3,6).
Normal anatomic variants
Prominent normal cardiac structures or embryological remnants,
such as crista terminalis,
eustachian valve,
right ventricular moderator band,
chiari network,
and prominent ventricular trabeculae,
can be mistaken for tumor (3,6).