Fetal cricotracheal manipulation: effects on airway healing, cricoid growth and lung development

The last decade has seen significant advance in the surgical management of pediatric subglottic stenosis, which remains one of the most fascinating problems of the laryngotracheal complex (LTC). Refined techniques for operating on these fragile structures should reduce cricotracheal scarring to a minimum, thus avoiding a lot of severe postoperative complications in a tricky moment of laryngeal's growing up. Experimental works indicates that the LTC growth is variously affected by longitudinal anterior, posterior or lateral incisions and actually the indications for laringotracheoplasty or cricotracheal resection in children with subglottic stenosis are still unclear. Reports on fetal manipulation of cricotracheal tissues are lacking as well as early effects on airway healing, LTC growth and lung development. The aim of this study was to evaluate if the airway mucosal healing is regenerative and scarless after cricotracheal manipulation in fetuses of New Zealand White Rabbits (NZWRFs). The consequences of fetal incisions on the cricoid growth and lung development are also examined, in a group of 12 NZWRFs, manipulated at 25+/-1 days of gestational age. The does underwent halothane anesthesia and all received a bilateral longitudinal cricoidotracheotomy. Twenty sham-operated fetuses were submitted to a limited cervicotomy (control's group). At the time of retrieval (31+/-0.5 days), en bloc laryngotracheobronchial tree and lungs were collected and processed for histological and morphometric analysis. Parameters recorded included: 1) histological full-thickness examinations focusing on inflammation, foreign body reaction, fibrosis, neochondrogenesis; 2) morphometric analysis, including the fetal Subglottic Diameter (FSD), the fetal Subglottic Area (FSA), the Radial Alveolar Count (rAC) and Computer Assisted Morphometric Colorimetry (CAmc); 3)analysis of lung hypoplasia (LH) by means of lung weight/body weight (LW/BW) ratio, protein and DNA indexes; 4) finally, different fractions of lung tissue phospholipids for lung maturity assessment were studied. Student's t test, when indicated, was performed for statistical analysis (p <0.05 = significant). There was no maternal mortality in this study. Ten fetuses were available for a final evaluation (16.6% mortality). In one case only, an incomplete closure of the fetal cricoidotomy was seen and could be probably due to a technical mistake. Mean fetal subglottic diameter and area were respectively 0.13+/-0.05 mm and 3.15+/-0.45 mm2 in both groups. As well as in fetal dermal repair, regeneration of the airway cartilage and mucosa were complete and scarless. LW/BW ratio, DNA content and analysis of different fractions of phospholipids were similar in experimental vs. the control group. These findings suggest that the healing processes were fibrosis-free and without evidence of scars. A complete closure of the incisions was achieved without stenosis of the fetal subglottic region. In addition, it seems that the fetal cricoidotracheotomy doesn't interfere with the laryngeal function which coordinate the amount of liquid leaving the lungs via the trachea. In addition, only a small leakage of amniotic fluid is shown and this could be responsible for normal and mature lungs.