Fetal Magnetic Resonance Imaging of Congenital Chest Malformations: A Pictorial Review

Congenital chest malformations may affect the foregut, pulmonary airway, vasculature, chest wall, and mediastinum. An understanding of fetal chest masses and their complications is essential for patient counseling, appropriate management of pregnancy, delivery, and neonatal care planning. Ultrasonography is the primary imaging modality used for the prenatal evaluation of chest malformations. Magnetic resonance imaging (MRI) is a well-established and complementary diagnostic tool in cases of inconclusive and inadequate findings of ultrasonography, particularly for the assessment of complex fetal abnormalities. In this study, we have reviewed the fetal MRI technique as well as discussed and illustrated the common congenital chest abnormalities observed by fetal MRI. Correspondence Author to: Yi-Lan Lin Department of Radiology, Mackay Memorial Hospital, Hsinchu, Taiwan No. 690, Sec. 2, Guang-Fu Road, Hsinchu 300, Taiwan J Radiol sci 2013; 38: 119-127 Fetal MRI of congenital chest malformations 120 J Radiol Sci December 2013 Vol.38 No.4 Types of congenital chest Malformations congenital Pulmonary Airway Malformation CPAM is the most common congenital lung malformation and accounts for 30-40% of all congenital chest diseases [2, 3, 6, 7]. It is characterized by adenomatoid proliferation of bronchiole-like cysts in the lung and a lack of normal alveolar development [7]. The term CPAM has been renamed as being preferable to the term congenital cystic adenomatoid malformation, since the lesions are cystic in only three of five types of these lesions and adenomatoid in only one type [4, 7]. These malformations may consist of cystic and solid components, resulting in various MRI manifestations. The findings of MRI depend on the size of the cysts. Typically, the signal intensity of the cysts is higher than that of the surrounding normal lung parenchyma [8-10]. Macrocystic CPAM appears as a lobulated mass with inhomogeneous hyperintensity (Fig. 1) [2, 9, 10], and microcystic CPAM as a lobulated mass of homogeneous hyperintensity with arterial vascular architectural distortion without visible cysts (Fig. 2) [6, 10]. Regression (either partial or nearly complete) of the masses in utero appears to be the rule. Regressed CPAM usually appears as an ill-defined inhomogeneous mildly hyperintense mass (as compared to the normal lung), which shows decreased signal intensity on follow-up MRI (Fig. 3) [9, 10]. The differential diagnosis for CPAM includes congenital bronchogenic cyst (single macrocystic CPAM), BPS, and CLFO (microcystic CPAM). bronchopulmonary sequestration BPS consists of nonfunctioning pulmonary tissue, which fails to connect to the normal tracheobronchial tree and receives systemic blood supply [9-13]. It is enveloped by the visceral lung pleura (intralobar subtype) or has its own visceral lung pleura (extralobar subtype). The majority of cases frequently occur in the lower lobes, especially in the left lower lobe [2-4]. MRI findings of pure BPS include a well-defined triangular homogeneous hyperintense mass with a higher signal intensity than that of a normal lung, but with lower signal intensity than that of the amniotic fluid, as well as visualization of the systemic feeding artery (Fig. 4) [2, 4, 8, 10, 11]. In the hybrid lesions of BPS and CPAM, the margin may be lobulated, and the signal is inhomogeneous and hyperintense (Fig. 5) [2, 6, 10]. BPS may also regress either partially or completely in utero. Regressed BPS tends to have a lobulated margin, with decreased and inhomogeneous signal intensity (Fig. 6) [10, 12]. The differential diagnosis includes microcystic CPAM and CLFO, and systemic arterial supply is the key finding for BPS [2, 3, 10, 11].