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Radiology
Sirenomelia
Built from Obstetric Imaging
What’s inside
9 sections · 65 slides
Overview
- Topics covered
What sirenomelia is
Definition, the name behind it, and the reason it is usually lethal
- Definition of sirenomelia
- Origin of the name
- Lethality and reported survival
- Core features of sirenomelia
- Preserved fetal specimen with fused lower limbs
- Embryoscopic view of fused lower limbs
The pattern of associated anomalies
What is found alongside the limbs, and the chain that follows absent kidneys
- Clinical presentation
- From absent kidneys to pulmonary hypoplasia
- Other reported anomalies
Classification schemes
Counting feet, counting bones, and a simpler scheme built for prenatal use
- Three ways of classifying sirenomelia
- Classification by the number of feet
- Sirenomelia types by the bones present in the limb
- Bone-based classification: types I to III
- Bone-based classification: types IV to VII
- Limits of the bone classification and a simpler scheme
Cord anatomy and the differential diagnosis
The single artery off the aorta is the feature that settles the diagnosis
- Single umbilical artery arising from the aorta
- Colour Doppler of a single umbilical artery from the aorta
- Vessels of a normal umbilical cord
- Sirenomelia versus caudal regression syndrome
- Differential diagnosis from imaging findings
Prevalence and epidemiology
How rare it is, the striking twin link, maternal diabetes and registry data
- 1.5-4.2
- Prevalence and the twin link
- Sex distribution
- Maternal diabetes as an association
- Findings of the international registry study
Cause, mechanism and embryology
Vascular steal, developmental field defects, teratogens, and the genes found by sequencing
- Failure of blastogenesis rather than fusion
- Vascular steal theory
- Vascular steal and its consequences
- Vitelline artery running from the aorta to the yolk sac
- Level of the vitelline remnant and the tissues affected
- Timing of the vascular insult
- Other disorders linked to vitelline vascular steal
- Primary developmental field defect theory
- Reported teratogens
- CYP genes in mouse models
- BMP7 and twisted gastrulation
- From sporadic event to genetic cause
- Exome sequencing findings
- CDX2, NKD1 and the Wnt signalling pathway
- Agreement between mouse models and human genetics
Imaging technique and findings
Why the first trimester scan wins, what a case series showed, and where MRI fits
- Ultrasound findings
- Limits of second-trimester ultrasound
- Advantage of first-trimester ultrasound
- Fused lower extremity on a 13-week ultrasound
- First-trimester case series: limb and bladder findings
- First-trimester case series: other findings
- Genetic testing in the first-trimester series
- Magnetic resonance imaging
- Fetal MRI of fused lower limbs
- Clinical value of fetal MRI
Management and outcome
Nothing to offer before birth, and what has been done for the few survivors
- Prenatal management and referral
- Reports of survival
- Postnatal surgical management
- Limb separation and later mobility
- What the referring physician needs to know
- Key points: features and diagnosis
- Key points: cause and outcome
- Suggested readings
- References
- References (continued)
- References (continued)
- References (continued)
- References (continued)
- Obstetric Imaging: Fetal Diagnosis and Care, 2nd Edition