Background: Congenital pulmonary airway malformations (CPAM) are rare developmental anomalies that may present with respiratory distress in neonates. Although generally benign, type 1 CPAM has been associated with malignant transformation, most often to adenocarcinoma. Such histological findings in the neonatal period are exceedingly rare and highlight the importance of early diagnosis, prompt intervention, and comprehensive pathological evaluation.Case Presentation: We present a preterm female neonate, born at 36 weeks of gestation by spontaneous vaginal delivery in cephalic presentation. Birth weight was 3020 g, length 49 cm, and head circumference 33 cm. Apgar scores were 9 at 1 minute, 6 at 5 minutes, and 7 at 10 minutes. Prophylactic intramuscular vitamin K was administered.At five minutes of life, the infant developed respiratory distress syndrome requiring mechanical ventilation. At approximately five hours, she deteriorated, necessitating advanced resuscitation. The neonatal course was further complicated by maternal–fetal infection (*Escherichia coli* blood culture), neonatal jaundice, transient hypocalcemia, and hypoglycemia.Initial chest CT revealed multiloculated fluid-density cystic areas occupying the lower two thirds of the right lung (maximum 51 × 44 mm), with left apical consolidation adherent to the heart and mediastinal deviation. A repeat CT described a large, multilobulated hypodense mass (60 × 44 × 58 mm), occupying almost the entire right lung and producing significant mass effect with mediastinal shift to the left.Surgical excision was performed. Pathology revealed: a) Interlobar lymph node - preserved lymphoid structure with sinus histiocytosis; b) Right upper lobe fragment - pseudocapsulated alveolar and bronchial proliferation with tubular and cystically dilated structures lined by pseudostratified columnar, partly ciliated epithelium. Architectural heterogeneity strongly suggested well-differentiated adenocarcinoma arising within a congenital cystic lesion. Immunophenotyping recommended for further characterization of pulmonary-type epithelial proliferation (CK7+, TTF-1+), displaying features consistent with well-differentiated mucinous adenocarcinoma arising in the context of type 1 CPAM.Learning Points:- CPAM may present with severe neonatal respiratory distress and require urgent surgical intervention.- Histological examination can reveal suspicious malignant features even in the immediate neonatal period.- Early resection not only relieves respiratory compromise but also provides a definitive diagnosis, underlining the importance of multidisciplinary evaluation and follow-up.- This finding underscores the rare but significant risk of malignant transformation within congenital pulmonary airway malformations, highlighting the importance of early surgical resection, detailed histopathological evaluation, and long-term follow-up.
