There is also a video (1.4 MB) that shows the anomaly a little better.
In this case the problem was not to identify the finding: everyone recognized that there was an extra cystic structure in the pelvis. Actually, during the original scan this was not quite so obvious since the pelvic bones were partially shadowing the bladder.
The difficulty of identifying the presence of a problem can be appreciated in the 8 first images. These were done after we had suspected the diagnosis. These images were obtained to maximize the visualization of the extra cyst and the bladder. When the extra cyst was suspected we obtained parasagittal views through the pelvis (the last 3 images).
The last 2 images demonstrated a normal spacing of the lumbar spine and the absence of spina bifida.
The normal cystic structure is the bladder that is the more anterior and superior cyst in the images. Note on the second image the umbilical arteries coursing around the bladder.
Importantly, there were no images of:
-
abnormal cerebellum and posterior fossa
-
distended loops of bowel
-
obstructed kidneys.
Therefore the findings were that of several cysts (2 were identified but several months later at surgery there were 4) that are posterior and inferior to the bladder.
Nothing much lives down there so here are the potential differential diagnoses:
-
an obstruction of the
-
gastrointestinal
-
urinary or
-
genital system
-
a spinal lesion such as:
-
anterior meningocele
-
internal sacrococcygeal teratoma
Differential diagnoses
A cloacal anomaly, an imperforated anus or a duplicated segment would not produce a clear cyst that early in the gestation. These condition are typically more likely to be visible in the later part of the pregnancy. They also tend to have low-level internal echoes.
A bladder diverticulum would be closer to the bladder and a connection to the bladder could be visible. Another urinary possibility could have been a hydronephrotic pelvic kidney, but no renal parenchyma is visible on any of the images.
A reproductive system lesion could be either an ovarian cyst, but this would be higher in the pelvis, or a hydrometrocolpos. A hydrometrocolpos might be in that region, but they tend to be more anterior in the pelvis (look on the magnified view how posterior this lesion is) and they too tend to have low-level echoes inside, not simply clear fluid as in this case. Further, a hydrometrocolpos would not have 2 cysts.
An anterior meningocele could certainly look like the lesion seen in the images, but more disruption of the lumbar spine would be expected, and also posterior fossa findings (banana sign, decrease of the cisterna magna) would be likely and none were shown.
The last common diagnosis would be an internal saccrococcygeal teratoma (Type IV). This was felt to be the more likely diagnosis for the reasons expressed above.
Postnatal findings
The CT was in agreement with the prenatal findings and the baby was operated on the second day of life. The mass was obstructing the rectum by compression.