The Double Threat: CMR Decoding of a Rare Type of Pediatric Myocarditis!

Description of Clinical Presentation: A 9-year-old girl with a history of asthma and allergic rhinitis presented with a 2-day of abdominal pain, low grade fever. CT abdomen ruled out appendicitis but showed the right pleural effusion, pericardial effusion, periportal edema prompting cardiac workup. EKG showed ST segment depression in inferior leads and elevation in anterior leads. Elevated Troponin-I 1.76 ng/mL, elevated BNP 313 pg/mL, elevated CRP 42.4 mg/L noted. Echocardiogram showed cardiac tamponade but preserved biventricular function. Urgent pericardiocentesis revealed cloudy yellow pericardial fluid with 54% eosinophils but negative infectious workup. Serum eosinophil counts increased on admission from < 1% to 10% 🡪18.8% 🡪35% in span of one week. Development of hypokinesia of anterolateral wall segments, borderline LV function on echocardiogram along with persistently elevated troponin-I prompted cardiac MRI evaluation.

Diagnostic Techniques and Their Most Important Findings: Contrast enhanced CMR with sedation was performed on a 1.5T GE Signa Artist (GE Healthcare, Chicago IL). Functional assessment with b-SSFP showed borderline LVEF (53%), significant hypertrophy (LV mass indexed 78 gm/m2) (Figure 1), mild hypokinesia of mid-inferior wall, normal RVEF (49%), and mild hypertrophy. Tissue characterization with T1 and T2 weighted sequences demonstrated elevated extracellular volume (ECV 43-54%) and elevated T2 values (58-79 msec) (Figure 2). Post gadolinium inversion recovery sequences at high inversion time (600 msec) showed hypointense basal/mid inferior and inferolateral wall segments. At usual inversion time (320-340 msec) the same area remained with well demarcated hypointense border and central hyperintensity. In addition, myocardial delayed enhancement of LV lateral, inferior and anterior wall segments noted with subendocardial, patchy and mid-myocardial pattern (Figure 2). Thus, in the presence of pericardial effusion modified Lake-Louis criteria for myocarditis were met.

CT angiogram of coronary arteries showed normal origin and course of left-dominant system although the right coronary artery was not well visualized beyond the conal branch. The patient received IVIG. Rheumatological, oncological and infectious (including parasitic) work up was negative. The CMR prompted treatment with steroids. Her LV function on echocardiogram returned to normal at 1-month follow up.

Learning Points from this Case: CMR imaging at high inversion time and delayed enhancement unmasked microvascular obstruction (MVO) which is a rare occurrence in children. MVO alerted us to differential diagnosis that included eosinophilic myocarditis (EM). Serum and pericardial fluid eosinophilia pointed towards possible EM. Our patient met all five published criteria for EM. Diagnosis of EM and MVO helped us define the prognosis. Thus, with the help of CMR imaging we decoded an extremely rare co-occurrence of “The Double Threat” - MVO and EM in a child.

Figure 1: Balanced steady state free precession short axis view (A) and 4-chamber view (B) of LV showing marked hypertrophy.
Figure 2: A. T2Weighted image short axis of LV showing increased hyperintensity (arrow). B. Post contrast Modified Look-Locker sequence showing area devoid of contrast uptake (arrow).
Figure 3: A. Inversion recovery image at higher inversion time of 600 msec showing area of microvascular obstruction (arrow) within the myocardial wall. Same area at usual inversion time of 300 msec (B), 320 msec (C) and 340 msec (D) (small arrow) showing well demarcated region of hyperintensity suggesting no contrast uptake. The long arrows indicate subendocardial to near transmural late gadolinium enhancement.