Congenital cystic adenomatoid malformation (CCAM), also known as congenital pulmonary airway malformation (CPAM), is a congenital bronchopulmonary anomaly characterized by the formation of cysts and abnormal dilation of the bronchioles. The cause of this condition remains unknown; however, it is probably related to transient airway obstruction and abnormalities in lung development during fetal life.^[1,2] It is a relatively rare condition, with an estimated incidence of 1 in 25,000 to 1 in 30,000 live births.^[3] Most cases of CCAM are detected during the prenatal or neonatal period; however, a later diagnosis during childhood or even adulthood is also possible, particularly in cases with less severe changes resulting in an asymptomatic course of the disease. Thus, the most common presentation of CCAM is a unilateral lung cystic lesion affecting one of the inferior lobes, typically detected in the early stages of life.^[4,5]CCAM may present clinically with various symptoms such as cough, fever, asthma, respiratory distress syndrome, hydrops fetalis, or spontaneous pneumothorax. In very rare cases, malignant transformation of the lesions into bronchioloalveolar carcinoma, adenocarcinoma, or pleuropulmonary blastoma may occur in adults. The CCAM classification developed by John Thomas Stocker divides the condition into three subtypes, and the updated classification divides CCAM into five subtypes, based on the morphology of the cystic lesions (Table 1).^[6,7]

The diagnosis of CCAM is based on chest imaging studies, such as X-ray, computed tomography (CT), or high-resolution computed tomography (HRCT). Since the condition most commonly affects newborns and children, suspicion can often arise prenatally during an ultrasound examination. The treatment of choice is surgical removal of the cystic lesion or the entire affected lobe.^[8] The aim of this study was to present a rare occurrence of CCAM type II diagnosed de novo in an adult, based on a case report and literature review.

This report describes a 43-year-old patient who was admitted to our thoracic surgery clinic because of abnormalities found on radiologic imaging. A chest X-ray revealed a large conglomerate of lesions, measuring 10 cm in diameter, located in the inferior lobe of the left lung. The patient had a history of recurring pneumonia, as well as arterial hypertension and hypothyroidism. He was in good overall health and did not report any symptoms such as cough, hemoptysis, shortness of breath, chest pain, fever, or reduced physical performance. Laboratory tests showed the following abnormalities: CRP 9.1 mg/L (reference range: 0.0–5.0 mg/L), glucose 107 mg/dL (70–99 mg/dL), and MCV 80.2 fL (82.0–98.0 fL), with normal hemoglobin levels. Arterial blood gas analysis revealed a decreased pO ₂ of 73.4 mmHg (reference range: 83.0–108.0 mmHg). Spirometry testing did not reveal any abnormalities. The chest X-ray performed in the posteroanterior (PA) projection showed a multicystic, air-filled, and encapsulated lesion in the left pleural cavity. The lesion did not cause a mass effect or mediastinal shift and showed no signs suggestive of fluid presence(Fig. 1A). A chest CT scan was also performed to confirm the suspicion and to determine the location of the lesion more precisely, as well as an angio-CT to detect possible pathological vascularization (Fig. 1B ).

The patient was eligible for surgery. Skin incisions were made for a video-assisted thoracoscopic surgery (VATS) procedure while the patient was under general anesthesia. After the left pleural cavity was opened, a macroscopic examination showed lesions in the posterobasal segment of the inferior lobe that were consistent with CCAM as seen on the CT scan (Fig. 2 ).

Due to the location of the lesion, it was decided to remove the affected lung parenchyma by performing an anatomical resection within the margins of the posterobasal segment and preserving segment VI of the inferior lobe(Fig. 3A–E). Additionally, a systematic mediastinal lymphadenectomy was performed, including thoracic lymph node stations 5, 7, 9, 10, and 11. The posterior hilum of the lung, the superior pulmonary vein, segmental vein V6, and the posterobasal vein were dissected. Segmental veins V8–V10 were cut using a surgical endostapler. The interlobar fissure just above the pulmonary artery was dissected, and its segmental branches A8–A10 were identified and secured with a surgical endostapler. Next, the segmental bronchi B8–B10 were dissected and also stapled. The remaining lung parenchyma was transected along the margins of the resected segment. Hemostasis was controlled, a drain was placed, and the retrieved material was sent for pathological examination. (Fig. 3F ).

The resected fragment of lung parenchyma measured 16.5×11.5×6 cm. On cross-section, most of the parenchyma was occupied by thin-walled cysts lined with ciliated epithelium, without signs of atypia. However, some cysts presented thick fibrous walls with focal micropapillary structures protruding into their lumens. Within the cysts, mucus and numerous foamy macrophages were observed. This microscopic appearance classified the lesion as CCAM type II. No neoplastic changes were detected in any of the examined lymph nodes. At the follow-up visit six months later, imaging studies showed no recurrence of the lesion. The chest X-ray did not reveal any suspicious disease foci, which was further confirmed by a control chest CT. Due to these findings, along with the absence of metastatic changes in the histopathological examination, there was no need for complementary treatment such as chemotherapy or radiotherapy.

CCAM is a rare hamartomatous lesion of the tracheobronchial tree with unknown etiology. Despite being uncommon, it proves to be responsible for approximately 25% of all congenital lung malformations. The incidence of this anomaly has demonstrated an upward trend in recent years, as evidenced by multiple population-based studies.‌^[5,11,14] Approximately 70% of these malformations are currently identified during routine fetal anatomical surveys. This apparent increase is most likely attributable to the expanded utilization of prenatal ultrasonography, coupled with advancements in imaging resolution that enable the identification of smaller pulmonary lesions during the antenatal period. One of the most frequently encountered diagnostic pitfalls is congenital diaphragmatic hernia, a condition with a significantly more guarded prognosis, particularly when confined to the left inferior lobe.^[10] It is worth mentioning that differential diagnosis of CCAM in adults may differ—bronchiectasis, bronchogenic cysts, and lung tumors should be taken into consideration, as they can also present as pulmonary cysts in CT.^[9,12] The lesions can also be misdiagnosed as chronic inflammation in both USG and CT but only in patients who present them after puberty, as inflammatory changes do not usually occur among children.^[12,14] Moreover, it should be acknowledged that in some cases detected prenatally, the defects do not follow the growth pattern or may undergo a complete spontaneous regression, referred to as “vanishing” lesions. Only 70 adult patients with CCAM diagnosed de novo were reported in English literature in 2022.^[9,10] In those patients, type I prevailed (75%), while type II was represented by 10-15% and type III—only by 10%.^[5,9,12] Adult patients with CCAM are frequently diagnosed either incidentally during routine physical examinations or in the context of recurrent pulmonary infections.^[9,12] Bacterial infection remains the most commonly reported complication of CCAM, frequently leading to acute febrile episodes and the formation of pulmonary abscesses. Only a few cases have been documented in which an aspergilloma exists within CCAM. What is noteworthy about CCAM is that late-onset CCAM in adults may present with increased radiographic complexity, which is frequently due to recurrent pulmonary infections that obscure or alter the typical imaging features.‌^[13] Information regarding clinical manifestations and surgical treatment of adult CCAM patients is limited due to its scarce presence. However, in such cases it is recommended to perform lobectomy or wedge pulmonary resection to prevent further infections and possible neoplastic transformation.^[9,12] Both VATS and posterolateral thoracotomy may be used as surgical techniques, and the choice between these operative methods is usually made with regard to the surgeon’s experience, although factors related to a patient can also be considered in the decision-making process.^[9,15] It has also been reported that performing a biopsy of the affected regions within the lesion can significantly increase the diagnostic accuracy, reaching a rate of 98.3%. In the literature, emphasis has been given to positive prognosis after the surgery, and it has been highlighted that there is no notable evidence of recurrence or metastasis postoperatively, but nevertheless, the patient should be attentively observed and the lymphadenectomy should be performed.^[14]

Although CCAM is typically detected in the prenatal or neonatal period, this report demonstrates that asymptomatic or minimally symptomatic cases may remain undiagnosed until adulthood, often discovered incidentally during imaging for unrelated issues.