Capillary apposition and density in the diagnosis of alveolar capillary dysplasia

Alveolar capillary dysplasia (ACD) is a rare disorder, typically presenting with persistent pulmonary hypertension of the newborn. The aim was to characterise further the histological features of patients suspected of having ACD and to correlate histopathological features with outcome.

Three pathologists retrospectively reviewed 21 surgical lung biopsy specimens (SLBx) where ACD entered the differential diagnosis. Semi-quantitative assessment showed that there was a spectrum of muscular arterial hypertrophy, capillary apposition to epithelium and capillary density within the interstitium, with the latter being more disordered in ACD. Misalignment of pulmonary vessels was also frequently seen. Four of 19 patients survived beyond the neonatal period, these having higher degrees of capillary apposition and density. Associated extrapulmonary abnormalities were common, most frequently with ACD.

Poor capillary apposition and density, allied with medial arterial hypertrophy and misalignment of pulmonary vessels are the strongest diagnostic features of ACD. Of the four patients alive, all had high capillary apposition and density, suggesting that these features may be of prognostic value. SLBx remains useful in such cases as it may help predict patients who survive the neonatal period and also identify patients with disorders that are not primarily vascular anomalies.