Histogenesis of Human Lung with Special Histochemical Stains in Aborted Fetuses at Different Weeks of Gestation

Abstract

Background: The lungs play a crucial role in gas exchange, supported by specialized cells

and tissues. While many studies have focused on the development of the human lung, limited research exists on the histogenesis of the human lung, particularly with the use of specific histochemical stains like Masson's Trichrome. Our study aims to address this gap by employing hematoxylin and eosin staining, along with Masson's Trichrome staining, on sections of aborted fetal lungs.

Materials & Methods: This cross-sectional observational study conducted at KAMS&RC, Hyderabad, and TS involved 77 aborted fetuses without congenital anomalies, aged between 12 to 40 weeks of gestational age. Lung tissues from the fetuses were collected after inevitable abortion, spontaneous miscarriage, stillbirth, or medical termination of pregnancy (MTP). The lung tissues were fixed in 10% neutral buffered formalin and subjected to Haematoxylin-Eosin (H&E) staining for general observations, and Masson's Trichrome staining to assess connective tissue deposition during lung development. The study aimed to provide insights into lung histogenesis in aborted fetuses using specific histological techniques.

Results: At 12-16 weeks of gestation, the lungs have abundant mesenchymal tissue, and the bronchi are lined by columnar epithelium. Between 17-20 weeks, bronchi are surrounded by hyaline cartilage. At 21-24 weeks, bronchial tubes are lined by simple cuboidal epithelium with cartilaginous islands in their walls. From 25-28 weeks, the mesenchyme reduces, and multiple branching bronchi with cartilaginous plates and lymphatics are evident. At 29-32 weeks, numerous air spaces with an increased capillary network are observed. At 33- 36 weeks, bronchioles with developing alveoli are seen. By 37-40 weeks, many alveoli separated by thin septa and a single layer of alveolar capillary network are present. Masson's trichrome stain was used to highlight connective tissue elements such as collagen and smooth muscle fibers around bronchi and blood vessels at various gestational ages. The study provides important insights into the morphological progression of fetal lung development throughout gestation.

Conclusion: In the present study, multiple staining methods were employed to document the appearance and organization of lung tissue during development in aborted fetuses at different gestational ages. As the gestational age advanced, a gradual decrease in the amount of mesenchymal tissue and the height of the epithelium was observed. Additionally, the study planned to investigate the expression of FGF-10 in the specimens. FGF-10 is a growth factor that plays a critical role in lung development, and its examination may provide further insights into the molecular mechanisms underlying fetal lung maturation at different stages of gestation.