Conduction system hamartoma (CSH) is a rare hamartomatous lesion more common in female infants.

CSH involves the proliferation and aggregation of Purkinje(-like) cells.

Germline mutations in nicotinamide adenine dinucleotide:ubiquinone oxidoreductase subunit B11 are World Health Organization-recommended diagnostic criteria for CSH.

Immunohistochemical analysis of mitochondria is a valuable diagnostic surrogate for mitochondrial cardiomyopathy including CSH.

Findings support mitochondrial dysfunction as a key pathogenic mechanism.

Conduction system hamartoma (CSH) is a rare cardiac lesion characterized by the abnormal proliferation of Purkinje-like myocytes. It predominantly affects female infants and is often associated with sudden cardiac death. Recent studies have linked mitochondrial dysfunction, particularly complex I deficiency, with CSH. We report an autopsy case of an eight-month-old female infant who died suddenly following mild gastrointestinal symptoms. A gross examination revealed mild cardiac hypertrophy without nodular lesions. Histological analysis identified multifocal aggregates of Purkinje-like cells with clear or foamy cytoplasm, some forming well-circumscribed nodules in the non-compacted myocardium. Immunohistochemistry demonstrated a marked reduction in complex I expression, supporting mitochondrial dysfunction. Although prominent trabeculations and deep recesses suggestive of left ventricular noncompaction were observed, they did not meet the strict diagnostic criteria. This case supports the potential role of mitochondrial complex I deficiency as a key pathogenic mechanism in CSH and highlights the significance of detailed histopathological and immunohistochemical analyses for an accurate diagnosis, especially in cases of sudden unexplained infant death.

Conduction system hamartoma

Autopsy

Mitochondrial cardiomyopathy

Infantile sudden death

conduction system hamartoma

nicotinamide adenine dinucleotide

left ventricular non-compaction

© 2025 The Author(s). Published by Elsevier Inc.