Closed spinal dysraphisms with a mass
These anomalies are often associated with midline cutaneous stigmata and accompanied by the presence of an intraspinal lipoma. It is believed that adipose tissue forms due to premature separation of the cutaneous ectoderm from the neuroectoderm (McClone hypothesis), resulting in contact between the mesenchyme and the open neural tube.
- Lipomyelocele (Lipomyelocele): the junction between the neural placode and adipose tissue is localized strictly within the spinal canal.
- Lipomyelomeningocele (Lipomyelomeningocele): the junctional zone extends outside the spinal canal.
Based on their growth pattern, lipomas are classified into dorsal (easily resectable), transitional (extending caudally), and “chaotic”. The latter type envelops the neural placode ventrally, is extremely difficult to resect, and is frequently combined with sacral agenesis.
Occult defects without a mass
This category includes simple intramedullary lipomas and pathologies of the terminal filament (filum terminale).
- Tight filum terminale syndrome (Tight filum terminale): the terminal filament is thickened (diameter greater than 2 mm) and shortened. This leads to an abnormally low position of the conus medullaris, its mechanical fixation, and tension, which causes neurological symptoms.
- Dorsal dermal sinus (Dorsal Dermal Sinus): an epithelium-lined fistulous tract extending from the skin surface inward. If the dimple is located above the intergluteal cleft and directed cranially, there is a high risk of communication with the dural sac. This condition requires surgery to prevent CNS infections. Sacrococcygeal dimples directed downward (caudally) are completely safe.
Meningocele and myelocystocele
Hernial protrusions can have different locations and contents:
- Posterior meningocele: a cerebrospinal fluid-filled sac covered by the dura and arachnoid mater, herniating through a posterior bony defect. Manifests as a skin-covered mass on the back.
- Anterior meningocele: typically presacral, accompanied by caudal agenesis. Manifests as lower back pain and pelvic organ dysfunction.
- Terminal myelocystocele: a rare anomaly (often seen in VACTERL association). The central canal of the spinal cord widens (forming a hydromyelic cavity) and prolapses directly into the posterior meningocele.
Notochord integration anomalies (diastematomyelia)
In diastematomyelia (Diastematomyelia), the spinal cord is longitudinally split into two halves (hemicords), each having anterior and posterior horns.
- Type I: the spinal cord is divided into two distinct dural sacs, separated by an extradural osteocartilaginous spur (osteocartilaginous spur).
- Type II: both halves are located within a single dural sac, separated only by a fibrous septum.
The most severe and rarest form of integration disorder is a neurenteric cyst (Neurenteric Cyst). It originates from endodermal remnants and is located intradurally ventral to the spinal cord, often passing through a ventral bony defect (Kovalevsky canal).
Disorders of caudal cell mass development
Pathologies in this group arise as a result of notochord cell apoptosis in the distal regions.
- Caudal regression syndrome (Caudal agenesis): a severe pathology resulting in the absence of lower vertebrae, a wedge-shaped truncation of the spinal cord, anal atresia, and genital anomalies. Associated with OEIS and VACTERL syndromes.
- Currarino triad (Currarino triad): includes a presacral cystic mass (meningocele or teratoma), a left-sided scimitar sacrum, and anorectal malformations.
- Segmental spinal dysgenesis: local underdevelopment of a short spinal segment with canal obliteration and acute kyphoscoliosis. However, functioning neural tissue is preserved below the level of the lesion.
Briefly: answers to topical questions
What clinical manifestations are typical for tight filum terminale syndrome?
Tight filum terminale syndrome is characterized by the development of clinical tethering (tethering) and a low-lying spinal cord. This pathology is a consequence of abnormal regressive differentiation. Morphologically, the syndrome manifests as a short and thickened terminal filament (tight filum terminale) with a diameter exceeding 2 mm. In the absence of clinical symptoms of tethered cord syndrome, fatty transformation of the filum terminale is considered a normal variant.
What anatomical structures are affected in caudal regression syndrome?
In caudal regression syndrome, the structures of the spine, spinal cord, as well as the gastrointestinal and urogenital systems are affected.
The pathological process involves the following anatomical structures:
- Vertebral column — absence of vertebrae at the affected level (variable aplasia ranging from coccygeal to lower thoracic vertebrae, partial sacral agenesis).
- Spinal cord — characterized by a truncated (truncated) structure, abrupt high termination, or partial conus agenesis.
- Anus — atresia of the anus (imperforate anus) occurs.
- Genitalia — various developmental anomalies are observed.
An easy way to remember the danger of sacral dimples: "Points up — surgeon gets a look, points down — safe and sound." A cranial tract direction threatens communication with the CSF space, whereas a caudal (downward) direction is safe.
Class and exam questions
What is the difference between lipomyelocele and lipomyelomeningocele?
In lipomyelocele, the junction between the neural placode and adipose tissue is strictly within the spinal canal. In lipomyelomeningocele, the junctional zone prolapses outward.
What is the key difference between type I and type II diastematomyelia?
In type I, the spinal cord halves are enclosed in two separate dural sacs and separated by a bony spur. In type II, they lie within a single dural sac and are separated only by a fibrous septum.
Does a sacrococcygeal dimple need to be operated on?
If the dimple is located below the intergluteal cleft, points downward, and there are no neurological symptoms, it is safe. Dimples located above the cleft with a cranial (upward) tract are surgically treated due to the risk of meningitis.
What else to study on this topic
- Clinical manifestations of tethered cord syndrome
- MRI findings of postoperative complications (retethering, syringomyelia)
- Differential diagnosis of presacral masses (teratomas vs. meningocele)
- Congenital neurometabolic disorders and hypomyelination
- Radiological patterns of X-linked adrenoleukodystrophy
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