What is the probable anomaly?
The most likely possibility is an esophageal atresia, which tends to occur with fistula.
What is the embryologic problem?
At 25 days, there is an outpouching from the forgut. This outpouching forms the respiratory diverticulum. As development continues, the respiratory diverticulum divides to form the primitive lung buds that will eventually branch and form bronchi and alveoli of the lungs. The branching lung buds lie within the pericardioperitoneal canals surrounded by a mesothelial lining. Eventually, the body cavities divide into peritoneal, pericardial, and pleural cavities. Where the respiratory diverticulum attaches to the foregut, esophagotracheal ridges form along the length of the connection. The ridges fuse to form an esophagotracheal septum. This division results in a separate tube anteriorly (ventrally)--the trachea, and a posterior (dorsal) esophagus.
Abnormal separation of the trachea and the esophagus leads to abnormal connections and/or atresias. The most common situation is one in which the esophagus ends in the midportion (atresia) and the distal esophagus is connected to the trachea near the carina (fistula). The result is a tracheo-esophageal fistula with atresia. Other combinations of atresia/fisulta are possible. One of the more serious situations occurs when there is a fistula between the upper esophagus and the trachea that allows food to pass directly into the respiratory system, leading to aspiration pneumonia.
Explain the high AFI.
Unlike oligohydramnios, where there is insufficient amniotic fluid from a urinary tract anomaly, polyhydramnios can result when there is impaired swallowing of the fluid. In utero, the amniotic fluid is swallowed and resorbed. Thus, abnormalities of the gastrointestinal tract which impair swallowing and passage of fluid can result in polyhydramnios. The lack of a stomach bubble on ultrasound suggests that there could be a block prior to the stomach. (A "double bubble" suggests a block in the duodenum from duondenal atresia.)
What is the karyotype likely to be?
46, XY TE fistula/atresia is most often unrelated to chromosomal abnormalities.
Name a condition in which the problem seen in this case can occur with other anomalies.
As always, the presence of one anomaly should alert you to the possibility that other anomalies are present. One pattern is the so-called VATER association. An association is not as well-defined as a syndrome, but describes features that are more frequently seen together.
V -- Vertebral anomalies
A -- Anal atresia
T -- Tracheal fistula
E -- Esophageal atresia
R -- Renal or radial anomalies
For the VACTERL association, add cardiac anomalies and limb anomalies.
Can this situation be treated?
A TE fistula/atresia can be repaired surgically. The presence of other anomalies may determine how practical this is.