Type:
Educational Exhibit
Keywords:
Diagnostic procedure, MR, Cardiovascular system, Cardiac, Blood
Authors:
V. Ojha, K. P. Ganga, G. S. Gulati, S. Seth; New Delhi/IN
DOI:
10.26044/ecr2019/C-2049
Background
Time of inversion scout (TIS) sequence,
performed to identify the nulling time of myocardium,
shows nulling of myocardium before blood pool in cardiac amyloidosis (reversed nulling pattern) as opposed to the normal pattern of nulling i.e blood followed by myocardium and spleen. However,
it is important to know the other temporal patterns of nulling of myocardium,
blood and spleen as multiple nulling patterns may be seen with cardiac amyloidosis.
Although,
endomyocardial biopsy is the gold standard for diagnosing cardiac amyloidosis,
it is an invasive procedure,
prone to sampling errors and has inherent risks of ventricular perforation and arrhythmia. Hence,
cardiac MRI (CEMRI) has become the investigation of choice.
Although there is a characteristic pattern of global subendocardial enhancement in amyloidosis,
TIS contributes to the diagnostic accuracy of CEMRI by demonstrating an reversal of normal nulling pattern with a sensitivity and specificity of 77% and 96% respectively (1).
Obtaining a single null point in cardiac amyloidosis is difficult as there is a nonhomogeneous nulling of myocardium due to spatial heterogeneity in myocardial amyloid deposition.
Due to a lack of a specific null point,
a characteristic diffuse subendocardial late gadolinium enhancement (LGE) pattern (which has a sensitivity and specificity of 93% and 95 % respectively) may not be seen in all cases of cardiac amyloidosis (2).
In the cases with an atypical and nonspecific LGE distribution,
an altered nulling pattern if seen in these cases helps in establishing the diagnosis.
There are multiple hypothesis for the cause of this altered nulling patterns (3).
Two of the most accepted theories are-
- An increase in myocardial extracellular space caused by amyloid deposition causes gadolinium retention and shortening of the myocardial T1 time.
- Gadolinium is extracted from the blood pool by the systemic amyloid load thus causing prolongation of the blood T1 time relative to the myocardium.
These two mechanisms are thought to be responsible for the shortening of the myocardial T1 relative to blood T1 following contrast administration.
As described previously (1),
temporal differences in nulling among the myocardium,
blood and spleen have been observed.
Based on this,
four different nulling patterns can be seen.
Type 1 (Normal pattern)
|
Blood nulling followed by myocardium with splenic nulling coincident with the myocardium
|
Type 2
|
Myocardium nulling preceding or coinciding with the blood pool and coincident with spleen
|
Type 3
|
Myocardial nulling non-coincident with the splenic nulling,
blood nulls before myocardium
|
Type 4
|
Myocardium nulled before or with blood and non-coincident with the splenic nulling
|
Fig.
1 demonstrates the Type 1 nulling pattern seen in normal patients.
In this observational study,
we determined the prevalence of different types of nulling patterns in endomyocardial biopsy proven cases of cardiac amyloidosis.