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2000-09-15-05 Answer to case of the week #34 © Ramm

Answer to Case #34

September 15-29, 2000

Submitted and discussed by Phillip Ramm, RDMS 

Hong Kong

This patient was referred to us with an outside report of spinal abnormality on her "routine" 18 weeks scan. The limbs (not shown) were normal. The skull had a normal echogenicity. 

Best "facial profile" obtainable. (The hand is incompletely visible but is normal). The image demonstrates the nose and upper lip. The lower lip and jaw are not in the same alignment, which strongly suggests micrognathia. This impression is reinforced by the generous amount of fluid in all images, compatible with a swallowing problem due to the micrognathia.

Several views of the spine at the thoracic and lumbar levels demonstrate nuchal thickening (yes i know that was easy...) but note also that the posterior elements of the spine are not visible. This can be due to an oblique section of course, or an anomaly. The image below labeled Section at the level of the abdomen clears the confusion and demonstrates that the soft-tissue behind the back are normal.

Section at the level of the abdomen.

The 2 last images have an incredibly obvious finding ... that is so difficult to find... Look carefully !

Usually at this point I give the answer... but this time I want those who have not found the last finding to discover it on yourself.

These are 2 sections in the chest. Please step back 2 meters (or 2 yards) away from your computer, and mentally tell yourself ALL the anatomical structures that should be in these 2 sections. Think that you are doing an autopsy and you start by cutting the skin then....

Only when you have found the finding (or spend at least 3 minutes to find it) should you go on. (I know I will get a bunch of emails again telling me: "Arghh, Philippe I cannot believe that I missed that !")

OK, when you have really tried,

Then  here are:

The findings:

The essential abnormal findings on the ultrasound were:

·        Total absence of ossification in the ribs and the posterior elements of the lower spine

·        Severe micrognathia

·        Receding forehead (possible)

·        Posterior nuchal edema

Further findings on autopsy performed after termination at 19 weeks were

·        U-shaped soft palate defect

·        Absent olfactory bulbs

·        Cribriform plate anomaly

On the initial scan the poor ossification of the ribs and spine made us consider some form of achondrogenesis, but the normal size and appearance of the long bones did not fit this pattern, plus the fact that the ribs were totally absent to our scanning, not merely hypo-ossified or fractured was against this differential diagnosis.  The severe micrognathia is consistent with something like Treacher-Collins or Nager syndrome, although it is a common finding in achondrogenesis.  Again it didn’t all fit together for us.  We did not detect the soft-palate defect in utero.

Searching the OMIM database for “micrognathia”, “nuchal oedema” and “rib absence” yields no result.117650 CEREBROCOSTOMANDIBULAR SYNDROME

The receding forehead was not commented on in the autopsy and it may be due to an oblique scan plan (it was hard to be certain of landmarks, plus baby was face down for most of the exam), however, once the palate defect and the intracranial anomalies were found at autopsy, the geneticists decided that the combination of findings in conjunction with normal long bones was consistent with a severe expression of the:

Cerebro-costo-mandibular syndrome

In the published cases, brain abnormalities are not always reported, and are quite variable, so the ultrasound findings described in this case are pretty much what sonographers should search for if a patient at risk for this syndrome presents for scanning in the late first or the second trimester.  In the third trimester, a bell-shaped chest and short ribs, distant form the spine, plus or minus rib fractures are to be expected.

There have been only two other reports of ultrasound findings in this syndrome but none showing the rib-less thorax quite as nicely as this case.

The patient represented with her next pregnancy at 12 weeks and this showed severe nuchal edema and severe micrognathia again.  It was too early to comment on the vertebral and rib ossification at this stage, we felt.  A mixed familial pattern of inheritance has been described for CCM syndrome, and the exact pattern of inheritance is undecided.

Histological analysis of the ribs showed slightly different appearances.  In the older fetus, ribs had cartilage anteriorly and a small amount of fibrous tissue postero-laterally.  In the younger fetus, there were gaps in the cartilage with primitive mesenchyme present posteriorly and laterally.  This might indicate some developmental process of the ribs in this syndrome, to give eventually the classic neonatal radiographic findings of “rib-gaps” in a patient with an apparent “flail chest”, which was the established way of diagnosing this syndrome. 

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