SPR Unknown #77 -- FINAL

Lucia Carpineta, M.D

Montreal Children's Hospital

Keywords

spr unknown 77, CCAM, CPAM, congenital, pulmonary malformation, sequestration, hybrid congenital lung lesion, prenatal MRI


Publication Date: 2012-10-12

History

32 year old woman. 28-week ultrasound found a left chest abnormality, and the heart on the right side. No hydrops. Prenatal MRI requested for further clarification. Images obtained at 31 weeks gestational age.

Findings

There is a normal amount of amniotic fluid. The left lung, and in particular the left lower lobe, is increased in size and the signal here is globally more hyperintense than normal on T2-weighted images, suggesting fluid trapping. Visceral situs is normal, but the descending aorta and the heart are slightly shifted toward the right (images 1, 2, 3), although the cardiac apex still points to the left (images 8, 9).

Within this hyperexpanded left lower lobe, scattered subtle further hyperintense rounded zones are noted, suggestive of tiny cysts, most notably within superior and posterolateral-basal segments (image 6).

Sagittal images close to the hilum (images 4, 5) demonstrate a prominent flow void extending unusually posterior and inferior. This abnormal prominent flow void extends inferomedially (image 2) and posteriorly (image 7) to connect with the aorta, indicating presence of an abnormal systemic feeding vessel arising from the aorta near the diaphragm.

The diaphragm and all other fetal structures were normal.

Diagnosis

CPAM - Hybrid congenital pulmonary malformation CCAM & sequestration (confirmed postnatally)

Discussion

Congenital pulmonary airway malformations (CPAM) is part of the bronchopulmonary/foregut malformation spectrum, and occurs in ~1:1500-4000 live births with a slight male prodominance. It accounts for approximately 25% of all congenital lung lesions. Until recently, it was referred to as congenital cystic adenomatoid malformation (CCAM). Initially Stocker classified these lesions into 3 types (macrocystic, microcystic and solid), but the latest widely accepted classification now recognizes 5 types, loosely based on Stocker’s initial scheme. Type 0 is of tracheal or bronchial origin, and therefore really represents more a type of acinar dysplasia. Type 1, the most common, comprises approximately 70% of cases, is of bronchial or bronchiolar origin, and contains large cysts varying between 2-10cm in diameter, although there may be additional smaller cysts nearby. Type 2, accounting for 15-20% if cases, is of bronchiolar origin, features smaller cysts measuring 0.5-2cm in diameter, and may be associated with pulmonary sequestration, renal abnormalities, and cardiac anomalies. Type 3 accounts for approximately 10%, is of bronchiolar-alveolar origin and features microcysts measuring less than 5mm in diameter not all of which may be visible, causing the lesion to have a hyperechoicsolid” appearance on prenatal ultrasound. Type 4, infinitely more rare, is of distal acinar origin and features unlined cysts which may be indistinguishable from a cystic pleuropulmonary blastoma.

The condition arises from abnormal development of the bronchoalveolar tree with pathologic hamartomatous proliferation of the terminal respiratory ducts and units (TRDU) in a gland-like fashion (hence the term adenomatoid) with cysts, but not normal alveoli. Unlike bronchogenic cysts, these arising cysts may communicate with the trachobronchial tree as well as with each other.

Most times, these lesions will involve a single lobe, although it is possible to involve more than one lobe, and the right middle lobe appears to be the least commonly involved. When small, these lesions may be undetected for years, when it is detected during workup for recurrent chest infections. Larger lesions are usually detected on antenatal ultrasound as a variably hyperechoic lung or part of a lung, occasionally with discernible cysts. Larger lesions will result in respiratory distress in the neonatal period, usually because of associated pulmonary hypoplasia in other portions of the lungs. The largest lesions have also been known to result in hydrops, polyhydramnios, and even congenital high airway obstruction syndrome (CHAOS) if there is significant associated mediastinal deviation.

Outcome in cases of CPAM is highly variable. There are rare reports of spontaneously regressing lesions. Most lesions, however, will remain stable in size. Smaller lesions may remain asymptomatic for long periods of time, and there is great controversy regarding whether these should be systematically excised because of the reported risk of associated malignancies. The associated malignancies in question include, notably, pleuropulmonary blastoma, but also bronchoalveolar and bronchogenic carcinoma. Larger lesions are usually symptomatic, either because of respiratory distress or recurrent infection, and are therefore excised (lobectomy) on an elective basis.

Files

References

  1. Stocker JT. Congenital pulmonary airway malformation: a new name for and an expanded classification of congenital cystic adenomatoid malformation of the lung. Symposium 24: non-neoplastic lung disease. Histopathology 2002; 41(suppl 2):424–430.
  2. Biyyam DR, Chapman T, Ferguson MR et al. Congenital Lung Abnormalities: Embryologic Features, Prenatal Diagnosis, and Postnatal Radiologic-Pathologic Correlation. RadioGraphics 2010; 30, 1721-1738.
  3. Gross GW. Pediatric chest imaging. Curr Opin Radiol. 1992; 4(5): 36-43.
  4. Tran H, Fink MA, Crameri J et al. Congenital cystic adenomatoid malformation: monitoring the antenatal and short-term neonatal outcome. Aust N Z J Obstet Gynaecol. 2008; 48(5): 462-466.

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