Human fetal lung morphometry at autopsy with new modeling to quantitate structural maturity.

OBJECTIVES: To demonstrate a simplified morphometric procedure, including a new model for acinar structural maturity, applicable to autopsy fetal lung and present reference values for these parameters.

STUDY DESIGN: Cases with autopsy consent for research were studied. To simplify analysis only critical morphometric parameters were measured to allow calculation of gas-exchange surface area.

SUBJECT SELECTION: A total of 58 fetuses, 16-40 weeks were included. Subjects were rejected with any condition predisposing to pulmonary hypo/hyperplasia, significant maceration, or if lung weight/bodyweight or microscopy identified pulmonary hypoplasia or lung growth disorders.

METHODOLOGY: Lungs were inflation fixed, weights and volumes determined, sampled, then returned to the body. Volume densities (VV ) of parenchyma/non-parenchyma and air-space/gas-exchange tissue, gas-exchange surface density (SV ), and total surface area (SA) were determined. The number, mean radius, and septal thickness of modeled airspace-spheres were calculated. Equations were generated for each parameter function of gestation and bodyweight.

RESULTS: From 16 to 40-week weights and volumes increased as power functions from ∼4 g/mL to ∼90 g/mL. Parenchyma/non-parenchyma changed little-75:25 (16 weeks) to 71:29 (term). Parenchyma was 10% airspace:90% tissue early and 50:50 by term. Gas-exchange SV increased from 175 to 450 cm2 /cm3 and total SA increased from 0.059 to 4.793 m2 . There were 3.31 × 106 airspace-spheres, 12 µ radius, septal thickness 30 µ at 16 weeks, increasing to 56.92 × 106 , 26 µ radius, septal thickness 13 µ by term.

CONCLUSIONS: Morphometry can feasibly be performed at autopsy, providing more informative quantitative data on lung structural development than current methods utilized. This reference data set compares well with published data.