Cystic tumours of the atrioventricular node (sometimes called “benign mesotheliomas of the atrioventricular node”) are rare lesions associated with sudden cardiac death.^1,2 A recent case provided several informative points regarding the nature of this lesion and best practice methodology within the coroner’s necropsy.

A 31 year old man, training for a marathon, collapsed and died suddenly without previous medical history. No system, including the heart, revealed pathology on macroscopic examination at necropsy. Toxicology and non-cardiac tissue histology were negative. However, tissue sampling of the cardiac conduction system revealed an 11 mm diameter cystic tumour of the atrioventricular node that blended into the nodal tissue and proximal His bundle (fig 1). Immunohistochemistry showed no reactivity with standard mesothelial markers (calretinin, thrombomodulin, and Wilms’ tumour 1), although reactivity for pan-keratin (AE1AE3), cytokeratin 5/6 (CK5/6), cytokeratin 7, epithelial membrane antigen, BerEp4, and carcinoembryonic antigen was noted. Mucin histochemistry, and staining for p53, Bcl-2, cyclin D1, CK20, and thyroid transcription factor 1 was negative. Mib-1 (Ki-67) staining showed minimal proliferation (2%). Previously reported immunohistology studies showed no reactivity with HBME-1 and antibody to factor VIII receptor antigen, and positive staining for secretory component and CA19.9.^3,4

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Figure 1

 Irregular glands (*) are seen running into the His bundle (H) tissue (original magnification, ×200; haematoxylin and eosin stain).

The immunohistochemistry profile appears to support epithelial differentiation, and designation of this tumour as a form of endodermal heterotopia. This probably reflects embryonic developmental factors, with differentiation towards an upper foregut phenotype. Certainly, these results provide confirmation that the lesion should not be regarded as mesothelial. Furthermore, immunohistochemistry could also argue against a neoplastic aetiology, thereby supporting the concept of a congenital tissue rest, capable of slow proliferation.

The precise incidence of this tumour cannot be determined given the infrequency of detailed examination of the cardiac conduction system at necropsy (in patients with and without cardiac disease) and the lack of macroscopic clues to its presence. Cases of sudden cardiac death have shown that this tumour is associated with fatal cardiac dysrhythmia, although partial/heart block has also been reported.^1,3 Patients with a more atrial based site appear to have a better presentation with heart block,^3,5 and in rare cases there is the possibility of surgical ablation.³ This case presented with sudden death, probably as a consequence of a re-entrant tachycardia/ventricular fibrillation. No preceding syncopal history was derived from relatives.

Investigation of these cases usually requires careful cardiac tissue sampling.¹ Recent adverse publicity with regard to the necropsy has disinclined some pathologists from carrying out postmortem histological investigations. In this case, the standard tissue blocks around the atrioventricular node, sinoatrial node, His bundle, and regional samples from both ventricles were taken after transfer of the heart to our centre from the primary hospital. The residual cardiac tissues were then returned, within 24 hours, to be reunited with the body, allowing for appropriate funeral arrangements without delay. Despite the perceived complexity of dissection of the conduction system, it is possible to sample tissues appropriately without creating problems for the coroner or relatives. Indeed, failure to take adequate histology will automatically mean the failure to make a vital diagnosis of relevance to an inquest.