The CRMR SPIN@ cares for patients with rare vertebral anomalies either isolated or associated with spinal cord anomalies (Spina Bifida and other Dysraphisms, SBoD) and vertebral segmentation anomalies (hemivertebrae, vertebral blocks, congenital bars, and sacral anomalies).
1) Spinal dysraphisms: “Spina Bifida and other dysraphisms” (SBoD).
Spinal dysraphisms (including spina bifida) refer to a group of rare neural tube closure defects affecting the vertebral column and spinal cord, occurring during early stages of embryonic development.
The classification of spinal dysraphisms distinguishes between open dysraphisms (formerly known as “spina bifida aperta”), closed dysraphisms (formerly known as “spina bifida occulta”) and borderline or frontier forms. These dysraphisms may have different characteristics, such as the presence of a posterior meningocele, a stalk or tract, fatty tissue (lipoma) or a split spinal cord.
(See the Orphanet page on “Spina bifida and other spinal dysraphisms”)
a. Open dysraphism
These are linked to a neural tube closure anomaly and are characterised by a cutaneous anomaly with exposure of the neural tissue in an area of the spinal column, with or without a sac of protuberance at the site of the lesion. Signs and symptoms vary depending on: the nature of the protrusion (which may represent only the meninges or also include spinal cord tissue and roots), the location, but may include motor, sensory and/or sphincter dysfunction, hydrocephalus and/or skeletal abnormalities (e.g. scoliosis).
Open dysraphism associated with a meningocele
Dysraphism characterised by a lack of skin covering, exposure of nerve structures to the external environment, and the presence of a saccular hernia containing cerebrospinal fluid through a posterior spina bifida (opening of the posterior vertebral arches). It is most often located in the lumbosacral region. A complete or partial Chiari II malformation is present in the cerebral level, which may be associated with ventricular dilatation (ventriculomegaly).
There are two main types of open dysraphism associated with a meningocele:
- Open dysraphism associated with a myelomeningocele(myelomeningocele, or MMC)
- Myelic limited dorsal malformation (MyeLDM)
Rarely, these types of open dysraphism may be associated with a duplication of the spinal cord, in the case of a hemi-myelomeningocele for example.
Open dysraphism without meningocele: myeloschisis
A myeloschisis is a form of dysraphism corresponding to an open neural tube defect characterised by the absence of a sac, dysplastic meninges and a neural placode exposed through a defect in the posterior vertebral arches (spina bifida) which is contiguous with the surrounding skin. The placode is at or below the skin plane and is typically associated with a Chiari II malformation. Myeloschisis is usually isolated (“true myeloschisis“) or, more rarely, associated with a split spinal cord (“hemi-myeloschisis“).
b. Closed dysraphism
A group of spinal dysraphisms, formerly known as “spina bifida occulta”, which vary greatly in severity. The skin overlying the anomaly remains intact, although the skin itself may be abnormal and present features such as a tuft of hair, a crater or a haemangioma. These skin features are known as “skin stigmata” of spinal dysraphisms.
Dysraphism with tract
Characterised by the presence of a stalk connecting the skin to the underlying spinal cord. The composition of the tract is variable and may contain non-functional neural tissue, fibrous mesenchymal tissue or dermal/epidermal elements. Depending on the nature of this tract, there are differents forms of dysraphism:
Dysraphic spinal cord lipoma
There are several types of lipoma, some of which are forms of dysraphism. This group of rare spinal cord lipomas is characterised by the presence of an extramedullary lipomatous mass which may be located throughout the spinal cord with or without a dural defect.
Isolated posterior meningocele
Rare neural tube closure anomaly A rare neural tube closure defect characterized by the herniation of a cerebrospinal fluid-filled sac, that is lined by dura and arachnoid mater, through a posterior spina bifida and covered by a layer of skin of variable thickness, which may be dysplastic or ulcerated. The spinal cord and nerves are generally not included and function normally, although sometimes a tethered cord may be associated. Toutefois, une moelle épinière attachée peut parfois être associée. They are usually located in the lumbar or sacral region.
Split cord malformation
A malformation characterised by localised division of the spinal cord into two “hemicords”, sometimes associated with vertebro-costal anomalies. It is most often a closed dysraphism, and a cutaneous stigmata may be observed in the form of focal hypertrichosis/hairy patch. This malformation may exist in an isolated form or in the presence of other dysraphic anomalies (e.g. filum lipoma). Depending on the nature of the separation between the two “hemicords”, different forms can be distinguished:
- Split cord malformation type I (or “diastematomyelia”)
- Split cord malformation type II (or “diplomyelia”)
In the very rare cases of forms associated with an open dysraphism, we refer to a split cord malformation of the “composite” type.
Myelocystocele
A rare, closed neural tube defect characterised by cystic dilatation of the central canal of the spinal cord, which herniates through an anomaly of the posterior vertebral arch (spina bifida) into a dural sac filled with cerebrospinal fluid (meningocele). It may be located in the caudal part of the spinal cord (terminal myelocystocele) or above the cone (non-terminal myelocystocele). The skin is intact or has stigmata.
Caudal regression syndrome
Rare congenital malformation of the lower segments of the vertebral column characterised by a truncated medulla or medullary cone, which may be associated with aplasia (or hypoplasia) of the sacrum and fusion of the iliac bones. Malformations of the gastrointestinal, genitourinary, skeletal and nervous systems are frequently associated.
c. Saccular spinal dysraphism associated with a posterior meningocele
This group of spinal dysraphisms is characterised by a meningocele containing a stalk connecting the spinal cord to the top of the meningocele. These saccular dysraphisms may be closed (terminal myelocystocele, Limited Dorsal Myeloschisis), open (myelominingocele) or borderline (MyeLDM). This stalk may be attached to the posterior surface and have a fibro-neural structure (in the case of saccular LDM) or may be the spinal cord itself (in the case of MyeLDM or myelomeningocele).
2) Vertebral and spinal abnormalities
a. Congenital dislocation of the rachis
Congenital dislocation of the rachis is a rare anomaly. This anomaly is characterised by an anterior defect in the formation of the vertebrae, with significant vertebral displacement and angulation of the spinal canal, leading to its narrowing or even interruption. This spinal anomaly is caused by an early embryonic mechanism. Prenatal diagnosis is important for parental counselling regarding the high risk of neurological consequences and postnatal management.
b. Abnormalities of vertebral segmentation, hemivertebrae
The hemivertebra is a defect in vertebral development that occurs during embryonic development. It is a frequent cause of congenital scoliosis. Most hemivertebrae have growth potential and can lead to scoliosis during growth, the degree of which depends on the type, location and size of the hemivertebra. The resulting asymmetric growth of the spine is responsible for congenital scoliosis.
Spondylocostal dysplasia, Costal segmentation anomalies
Spondylocostal dysplasia is a rare genetic disorder characterised by defects in the formation of the bones of the spinal column (vertebrae) and abnormalities of the ribs. The ribs may be fused or missing, with varying degrees of severity. These malformations are present from birth. The severity and specific symptoms may vary between affected individuals, even between members of the same family. Some infants may have difficulty breathing because of the reduced size of the thorax. Sometimes, breathing difficulties can be severe and life-threatening. Most often, spondylocostal dysplasia is inherited in an autosomal recessive manner and is caused by a change (mutation) in one of four genes, DLL3, MESP2, LFNG, HES7. Rarely, spondylocostal dysplasia can be inherited in an autosomal dominant fashion. One gene, TBX6, is known to cause dominant spondylocostal dysplasia. Many individuals have no mutations in any of these genes. Treatment of severe forms is difficult and is essentially aimed at achieving the best possible lung function in adulthood.
Sacrum anomalies and caudal pole malformation
Caudal regression syndrome, or sacral agenesis (or hypoplasia of the sacrum), is a rare congenital anomaly. It is a congenital anomaly in which the foetal development of the lower part of the spine, the caudal pole of the spine, is abnormal. The incidence is approximately one birth per 60,000. Clinical signs vary widely depending on the severity of the malformation, which can range from partial absence of the coccyx regions of the spine to absence of the lower vertebrae or even the pelvis. In some cases, where only a small part of the spine is missing, there may be no clinical signs, particularly neurological ones. In cases where larger areas of the spinal column are absent, there may be paralysis and hypoplasia of the lower limbs, fused joints and skin webbing (pterygium). Digestive and genito-urinary neurological damage may also be associated in severe forms.