Cystic tumor of the atrioventricular node in a patient with intermittent complete heart block

Abstract

© BMJ Publishing Group Limited 2021. No commercial reuse. See rights and permissions. Published by BMJ. DESCRIPTION A 55yearold man presented with occasional shortness of breath and palpitations for the last 6 months. Holter monitoring revealed intermittent complete heart block and junctional escape rhythm. Transthoracic echocardiography was unremarkable. Cardiac MR was performed to look for any scar or any other structural cause for palpitations. It revealed a 1.2×1 cm nodular lesion at the anterior mitral leafletinteratrial septal junction. This lesion appeared isointense on T1W images, hyperintense on T2W images and showed peripheral rim enhancement with a central dark core on late gadolinium enhancement (LGE) images (figure 1A–C). T2 mapping values were also raised (65 ms). On high TI (Inversion Time) LGE images, the lesion was relatively bright. Subsequently, CT angiography was also performed for the assessment of coronaries and to look for any calcification within the lesion. CT demonstrated the lesion with an attenuation of ~70 HU (Hounsfield Units) on the noncontrast CT with no significant enhancement observed in the postcontrast scans (figure 1D–F). Coronary arteries were normal. On the basis of morphological characteristics, the mass was presumed to be benign. Considering the unusual location of the mass, differential diagnosis included benign lesions like hamartoma, fibroma, cystic tumour of the atrioventricular node (CTAVN) and bronchogenic cyst. However, considering the signal characteristics and the location of the mass as well as patient’s symptoms, a likely diagnosis of CTAVN was made. Excision of the lesion was suggested; however, the patient did not opt for the same. Subsequently, pacemaker implantation was done and the patient is on the routine followup. CTAVNs are extremely rare congenital lesions located at the base of the interatrial septum. Because of their location, these masses often cause complete heart block and arrhythmias and may result in sudden cardiac death. These tumours have mostly been diagnosed postmortem with only a few antemortem reports in the literature. CTAVNs are generally small and the patients may remain asymptomatic or may present with palpitations, dizziness and dyspnoea. They may have variable signal intensity on CT as well as MRI depending on the composition of the microcysts and the amount of fibrous component. Fiset et al described a similar case of a 51yearold woman with thirddegree atrioventricular nodal block and junctional rhythm. Echocardiography revealed an echogenic mass at the same location as in our case, which showed a softtissue attenuation (63 HU) on CT. Although signal intensity on the noncontrast MRI was similar to our case, the lesion showed intense contrast enhancement. However, absence of postcontrast enhancement has also been reported in other similar cases. Although rare, a mass at this unusual location (at the base of the interatrial septum) should alert the radiologists to the possibility of this tumour as a differential diagnosis. It must however be emphasised that a tissue diagnosis is necessary Figure 1 T1weighted image (A), T2weighted image (B) and delayed post gadolinium image (C) in the short axis view demonstrate a 1.2×1 cm nodular lesion (indicated by white arrow) at the anterior mitral leafletinteratrial septal junction appearing isointense on T1weighted images, hyperintense on T2weighted images and showed peripheral rim enhancement with a central dark core on delayed post gadolinium image. Noncontrast CT image (D) and CT angiography images in the arterial phase (E) and delayed phase (F) depict high attenuation (approximately 70 Hounsfield Units (HU)) of the lesion (indicated by black dotted circle) with no significant postcontrast enhancement in the arterial or delayed phase.