Heron Werner, MD & Pedro Daltro, MD
Clínica de Diagnóstico por Imagem (CDPI) & Instituto Fernandes Figueira (IFF) – FIOCRUZRio de Janeiro – Brazil

Dorothy I. Bulas M.D.
Professor of Radiology and Pediatrics
Children's National Medical CenterGeorge Washington University Medical Center
111 Michigan Ave, NW,   Washington D.C. 20010

Diaphragmatic hernia is defined as a group of diaphragmatic defects in which part of the abdominal content move into the thoracic cavity (table 1).

Table 1: Diaphragmatic hernia

* bad prognosis

Pulmonary hypoplasia is one of the serious conditions that causes high mortality and morbidity in neonates ^1,3. Among the causes of pulmonary hypoplasia, such as acute oligohydramnios, skeletal malformations, intrathoracic masses and neuromuscular disorders, the diaphragmatic hernia stands out as one with the highest incidence (1 out of 3,000 to 4,000 live births/year), with a mortality rate nearing 70 percent ⁹. Although the prenatal diagnosis of pulmonary hypoplasia assists with the postnatal care of affected children and contributes to decision making in the obstetric management of the mothers, fetal ultrasound has only a limited role. The MRI can provide additional information about the anatomical details of malformed fetuses. Kuwashima et al (2001) evaluate pulmonary hypoplasia in 23 fetuses (18 – 40 weeks) with MRI. They used 1.5 T magnet and half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences. All of the fetuses studied with normal pulmonary development showed high intensity in the lung, except for one fetus at 24 weeks gestation, and all fetuses with pulmonary hypoplasia showed lung of low intensity. The association of hydrops and diaphragmatic hernia is rare but often results in death. Hydrops appears to be associated with liver in the hernia ¹¹.

The CNS malformation associated with diaphragmatic hernia lies around 30 percent ⁹. The cystic adenomatoid malformation of the lung is one differential diagnosis for diaphragmatic hernia. Such a diagnosis is often hardly obtainable, being necessary to resort to serial ultrasonography ³.Bargy & Sapin (1995), forerunners of the corrective surgery for intrauterine diaphragmatic hernia, analyzed 60 prenatally diagnosed cases of hernia. They observed a survival rate of 10 percent in cases where the transverse diameter of the thorax was inferior to percentile 10 and part of the liver herniated to the thorax. Ultrasound enables accurate diagnosis for congenital diaphragmatic hernia. However, the ability to do this diagnosis and determine the liver position depends on the skill of the examiner. The definitive diagnosis of congenital diaphragmatic hernia relies on visualization of the abdominal organs in the chest. The size of the amount of herniated viscera are difficult to quantitative only with ultrasound. We can suspect about the presence of the part of the liver in the chest when, by ultrasound, the stomach is in posterior or mid thoracic position. We can also use de Color Doppler flow to observe the umbilical and portal vasculature.

The MRI can show clearly the herniation of fetal liver into the chest. Hubbard et al. (1997) evaluated three gestation"s of 20, 23 and 32 weeks with left-sided diaphragmatic hernia. In all three cases, resonance could clearly show the liver position in the thorax. Nevertheless, in one of the cases, ultrasonography could also visualize the liver in the thorax. In our casuistic, we evaluated seven fetuses with left-sided diaphragmatic hernia. The left hepatic lobe was visualized in the hernial content by MRI in five fetuses, all of whom died after birth. These postnatal deaths confirms a poor prognosis for hepatic herniation. One of the fetuses had also a partial agenesis of vermis cerebellar with a karyotype confirming trisomy 18 ^12.

Leung et al. (2000) issue a detailed description of MR images of the different types of diaphragmatic hernia. Left-sided hernias are the majority of  cases, and ultrasonography easily visualizes the stomach and loops in the fetal thorax.
 When magnetic resonance is performed, the stomach is detected as a structure with a enhanced signal on T2. The intestinal loops are showed as tubular structures with a low signal on T1 and a high signal on T2. The varied intensity of signal on T1 and T2 is probably due to the presence or absence of meconium, what allows the identification of small intestine loops and colon. This is possible because in this last segment the quantity of meconium is bigger, leading to a low signal on T2. The cardiac displacement to the right and the pulmonary compression are both well visualized in the axial plane.

Approximately 83% of congenital diaphragmatic hernias are left-sided. They can have a part of the liver in their content in around 57 to 86 percent of cases (liver-up). A correct assessment of the actual position of the liver is of the most importance, for the death rate varies from 57 percent, if part of the liver is herniated, to 7 percent, if the liver is topical (liver-down)9. Hernias with a part of the liver in their content can be easily pinpointed given signal preservation in both the axial and coronal planes by MRI. The liver has an anterior position and displaces so the stomach upwards. It is also possible to visualize the gastric volvulus when we identify the arrangements of both the greater gastric curvature and the lesser gastric curvature. The sonographically determined LHR has also emerged as a good prognostic indicator for prenatally diagnosed liver-up. It is determined by obtaining a transverse axial image through the chest at the level of the four-chamber view of the heart at a gestational age of 24 to 26 weeks. An LHR of less than 1.0 is associated with 100% mortality, whereas an LHR of greater than 1.4 is associated with no mortality. For LHRs between 1.0 and 1.4, the mortality is approximately 60% ¹⁰.

Approximately 12 percent of hernias are right-sided9. In every diagnosed case, part of the liver is found inside the thorax. Visualization of loops inside the thorax is, in such a case, rather improbable. Right-sided hernias account for a high mortality rate of around 80 percent and is often accompanied by ascites as well as hydrothorax. This fact is probably due to an obstruction of the hepatic veins 9. MRI can be helpful in the determination of liver position and confirmation of diagnosis. Hedrick et al (2004) reviewed prenatal diagnostic studies (ultrasound, MRI and echocardiography) and pre- and postnatal outcomes in 22 cases of right-sided hernia. The postnatal survival rate was 83%, although many of these patients had long-term developmental, pulmonary, and gastrointestinal issues that have required re hospitalizations and ongoing care. Associated anomalies were common, such as cardiovascular (ventricular septal defect, pulmonary artery stenosis, right anomalous pulmonary venous return, interrupted inferior vena cava), central nervous system (microcephaly, Dandy-Walker malformation), extra lobar pulmonary sequestration, gastrointestinal (choledochal cyst, Meckel's diverticulum, omphalocele) and genitourinary (hydronephrosis, horseshoe kidney). They report no karyotype abnormalities.

In about 5 percent of cases, the diaphragmatic hernia can be bilateral9. The ultrasonographic diagnosis is difficult since there is no mediastinal shunt. Besides, the hepatic parenchyma mimickes the pulmonary tissue. MR can, in these cases, identify the hepatic herniation in either hemithorax from the different signal intensities on T1 and T2.

There are others images findings associated with diaphragmatic hernia such as polyhydramnios. It happens in 29% to 76% of cases ^5,9. The main cause is probably the less fetal swalling of amniotic fluid, which can be seen on MR imaging. The hypothesis that it is associated with a poor prognosis has not been confirmed by recent studies ⁴.
 In summary, the MR imaging can help the ultrasound to identify clearly the liver position and to evaluate the pulmonary hypoplasia.

References

1) Adzick SN, Harrison MR, Glick PL, Nakayama DK, Manning FA, DeLorimier AA. Diaphragmatic hernia in the fetus: prenatal diagnosis and outcome in 94 cases. J Pediatr Surg 1985; 20:357-361.
2) Bargy F, Sapin E. Pathologies intrathoraciques. In: Papiernik E, Cabrol D, Pons JC. Obstétrique. Flammarion, Paris 1995; 287-312.
3) Benacerraf BR, Adzick NS. Fetal diafragmatic hernia: Ultrasound diagnosis and clinical outcome in 19 cases. Am J Obstet Gynecol 1987; 156: 573-576.
4) Guibaud L, Filiatrault D, Garel L. Fetal congenital diaphragmatic hernia: accuracy of sonography in the diagnosis and prediction of the outcome after birth. AJR 1996; 166: 1195-1202.
5) Harrison MR, Mychaliska GB, Albanese CT. Correction of congenital diaphragmatic hernia in utero IX: fetuses with poor prognosis (liver herniation and low lung-to-head ratio) can be saved by temporary tracheal occlusion. J Pediatr Surg 1998; 33: 1017-1023.
6) Hedrick HL, Crombleholme TM, Flake AW, Nance ML, Von Allmen D, Howell LJ, Johnson MP, Wilson RD, Adzick NS. Right congenital diaphragmatic hernia: prenatal assessment and outcome. Journal of Pediatric Surgery 2004; 39(3): 319-323.
7) Hubbard AM, Adizick NS, Crombleholme TM, Haselgrove JC. Left-sided congenital diaphragmatic hernia: value of prenatal MR Imaging in preparation for fetal surgery. Radiology 1997; 203: 636-640.
8) Kuwashima S, Nishimura G, Iimura F, Kohno T, Watanabe H, Kohno A, Fujioka M. Low-intensity fetal lungs on MRI may suggest the diagnosis of pulmonary hypoplasia. Pediatr Radiol 2001; 31: 669-672.
9) Leung JWT, Coakley FV, Hricak H, Harrison MR, Farmer DL, Albanese CT, Filly RA. Prenatal MR Imaging of congenital diaphragmatic hernia. AJR 2000; 174: 1607-1612.
10)  Sydorak RM, Goldstein R, Hirose S, Tsao K, Farmer DL, Lee H, Harrison MR, Albanese CT. Journal of Pediatric Surgery 2002; 37(12): 1678-1680.
11)  Sydorak RM, Harrison MR. Congenital diaphragmatic hernia: advances in prenatal therapy. Clin Perinatol 2003; 30: 465-479.
12)  Werner H, Daltro P, Domingues RC, Brandão L, Brandão A, Pereira LR, Guerra F. Ultrafast magnetic resonance (MRI) in fetal diagnosis. In: Perinatology. Bologna (Italy), Monduzzi Editore, 2001; 733-738.