Introduction

One of the rare disorders that affects the lower spine and the spinal cord is called caudal regression syndrome (CRS). CRS is a rare genetic disorder that causes abnormal development when the foetus is still in the uterus. This disorder can cause abnormal development to different degrees, which affects how the lower limbs, genitourinary system, and gastrointestinal tract are formed.

However, CRS can be detected early during the prenatal stage, which can then increase potential positive outcomes as it allows for better and more prepared delivery planning, postnatal care preparation and parental counselling. This article shall focus on the prenatal detection of CRS using scans such as ultrasound and magnetic resonance imaging (MRI).

Understanding caudal regression syndrome

CRS is a condition which is most commonly associated with and linked to maternal diabetes; however, it can also present itself due to specific genetic factors. CRS itself can range in its severity of presentation from the lack of some bones within the coccyx, to complete abnormality within the formation of the sacrum, coccyx and lumbar spine.¹

CRS can also present itself alongside other abnormalities within an individual that involve the kidneys (renal dysplasia), anus (imperforate anus), or the feet (clubfoot). This can be due to the time at which each of these develops for the foetus when it is within the uterus.²

Role of prenatal ultrasound in detection

For any kind of prenatal scan, ultrasound is the first-line imaging (or scanning) tool that is used. It is a screening tool that is used at different stages of pregnancy to ensure that the foetus is developing well, and to identify any abnormalities or anything where an intervention, or interventions, may be needed.

When specifically screening for CRS within prenatal ultrasound, there are some key findings that may be found if the foetus is thought to show signs of CRS. The findings on ultrasound may include, but are not limited to:³

• Deformities within the lower limbs
• Missing or underdeveloped sacral and lumbar spine vertebrae (bones)
• Abnormalities regarding the bladder
• Abnormalities regarding the kidneys
• Unexpected end to the spine

The stage of pregnancy in which it is best to detect and assess these possible abnormalities is typically within the second trimester of pregnancy (weeks 13 to 27 of pregnancy). Although this is the optimal time to detect the possibility of CRS through ultrasound scans, more severe forms of CRS may be able to be seen earlier and therefore identified earlier in a foetus’s development.⁴

Advantages and limitations of ultrasound

When thinking about the overall advantages of using ultrasound as an investigation method, there are three main ones that are at the forefront. These include that it is a non-invasive procedure, it is an imaging option which is widely available, and it is a safe method of scanning throughout the whole of the pregnancy. However, there are limitations to this method of scanning – these revolve around the lack of visualisation within ultrasound images. More mild or subtle forms of CRS may be tricky to identify purely by ultrasound, and generally, ultrasound poses limitations in the visualisation of complex spinal abnormalities, particularly in later weeks of gestation or in those with maternal obesity.

Role of prenatal MRI in diagnosis

MRI is not typically used as a first-line measure in foetal medicine, primarily due to its higher cost, limited availability, and longer scanning times compared to ultrasound (which is first-line). Foetal MRI would be an appropriate imaging method when trying to get a clearer picture of findings seen within an ultrasound scan, or as a tool to allow for a better definition of the extent of abnormalities which are present. Foetal MRI is simply a complementary tool to ultrasound.⁵ If a foetal MRI is needed to assist with the visualisation of certain organs and processes within the body alongside an ultrasound, then it is typically carried out within the second or third trimester (weeks 13 to 27 of pregnancy, and weeks 28 to 40 of pregnancy, respectively).

Within the role of foetal medicine, and CRS specifically, MRI allows for a better visualisation of soft tissue compared to ultrasound, as well as being able to formulate and visualise images within several planes. Due to the superior visualisation and contrast of soft tissue, this method of imaging is a better diagnostic tool for CRS, as soft tissue is the type of material which makes up the spinal cord, brain, and pelvic organs (crucial areas to see abnormalities in to assist with the diagnosis of CRS). When looking at the spine and using an MRI on a foetus who is thought to have CRS, it is possible to confirm and clarify the level at which the spine terminates. MRI can also assist in the overall severity of abnormalities present with CRS and can confirm or rule out any additional abnormalities associated with a CRS diagnosis.⁶

Counselling and management following diagnosis

As soon as there is a diagnosis of CRS, a team of professionals across the multidisciplinary team (MDT) will be involved in the overall care of the child. These members of the MDT will likely include: obstetricians, geneticists, paediatric specialists and radiologists. Within these specialities, there will be many subsections of the professional work force, like doctors, nurses, allied health professionals, therapists, to name a few. It is crucial to have all these MDT members involved in order to optimise the care for the child in a holistic sense and to ensure all aspects of CRS are considered. 

Alongside help and care from these professionals, parents will receive comprehensive and consistent psychological assistance and counselling in order to support them through the choices they will need to consider and make for perinatal care, any concerns or queries regarding prognosis and for general support regarding the expected outcomes of their child.⁷ Depending upon the findings of previous testing and imaging, genetic testing or further investigations may also be offered to the family, which may assist with any future family planning.  These investigations may also guide future management for any of their children who may have CRS. 

Plans for the delivery of the baby will also need to be discussed in depth, as it may be important to involve doctors within a hospital setting that has both a neonatal intensive care unit (NICU) and the facilities and staff for neonatal surgery (rather than a midwife at home, or a hospital without these capabilities and facilities).

Summary

Caudal regression syndrome (CRS) is a rare disorder that manifests itself as abnormal development. It is possible to identify CRS during the prenatal phase through the use of both ultrasound scanning and MRI in a complementary manner. Being able to identify and diagnose CRS prenatally helps professionals to plan in the best way they can for both the delivery and care of the child; this, in turn, can also increase the possibilities of more positive postnatal outcomes. Ultrasound scanning is the first-line scanning method used for the prenatal diagnosis of several conditions, including CRS, and then MRI assists in the visualisation of important details within the images regarding the severity, complexity and if there are any uncertainties regarding that specific case or diagnosis of CRS. 

Overall, once CRS is suspected and eventually diagnosed, there will be a multidisciplinary team that will coordinate to best support the child both pre- and post-delivery, as well as through their lifetime. Alongside this, parents will be supported every step of the journey through psychological assistance and counselling. All of these stages are important to help ensure that this rare condition is managed effectively and optimally, which in turn increases the potential for positive outcomes for the child with CRS.

Frequently asked questions (FAQs)

When can CRS first be detected during pregnancy?

Due to the need for certain organs and structures of the foetus to be developed, the best time within pregnancy to first identify CRS is within the second trimester (weeks 13 to 27 of pregnancy).

What signs on ultrasound may suggest CRS?

If these abnormalities are seen within an ultrasound scan, CRS may be suspected:

• Deformities within the lower limbs
• Missing or underdeveloped sacral and lumbar spine vertebrae (bones)
• Abnormalities regarding the bladder
• Abnormalities regarding the kidneys
• Unexpected end to the spine

(This is not a conclusive list, but these are the typical abnormalities seen within CRS.)

Why is an MRI recommended if an ultrasound already shows abnormalities?

Foetal MRI is recommended even when an ultrasound shows abnormalities, due to the fact that MRI is a better imaging tool to see soft tissues within the body. Specific to CRS, the spinal cord is better visualised using MRI compared to ultrasound. MRI can then be used to confirm and clarify the level at which the spine stops, and the severity of presentation within the spine and other organs involving soft tissues.

Is CRS always linked to maternal diabetes?

No, it is not always linked to maternal diabetes (otherwise known as gestational diabetes). CRS is, however, most commonly linked to maternal diabetes, but there are also genetic causes of CRS.