These lesions are often diagnosed at childbirth or in young children because of the associated midline deformity,
but it is not uncommon to find adults with an undiagnosed spinal dysraphism which only comes to be clinically apparent when the patient presents with some form of neurological deficit.
They are thought to arise from the accidental entrapment of mesenchymal cells in the midline,
but it is now known that this is an oversimplification of the embryological development of the disease since the lipomatous portion often contains other tissular components in different ratios and not only adypocites.
The lipomyelomeningocoeles is more often found at a sacral level and is usually continuous with the subcutaneous fat,
protruding through a bony defect and blending with the dura.
The cord is typically found at a lower spinal level and attached to the lipoma.
They are principally found in the midline extending to the buttock in a asymmetrical fashion and are accompanied by a range of cutaneous,
orthopaedic and urinary syndromes as well as other related anomalies that will be further described.
By contrast to other closed dysrapishm,
a Chiari II malformation is seldom encountered.
Epidemiology:
Both environmental and genetic factors coexist in the pathophysiology of spinal dysraphisms.
Unfortunately no relation between the reduction in lipomylomeningocele rates and increased maternal dietary acid folic intake has been proved.
It is thought to be more common in babies born to younger mothers,
hispanics,obese mothers,
while familiar forms are rare
The true prevalence is not established and different authors report a range of different incidences but it is thought to be around 1 per 4,000 live births (US),
with a clear female predominance,
with a ratio of 1,5:1 (female to male).
Diagnosis and presentation:
Lesions are often diagnosed in infancy because of the associated midline deformity ( an asymmetrically positioned fatty mass in the lumbosacral region) and its accompanying skin lesions .
This allows prompt recognition and some authors report that 48% of patients are neurologically intact at the time of diagnosis.
Although as previously mentioned it is not uncommon to find adults with an undiagnosed spinal dysraphism which becomes apparent after the patient develops a neurological deficit.
In lipomyelomeningocele the spinal defect is associated to a subcutaneous lipofibrous mass that is adjacent to a elongated and rotated segmental placode that bisects the lumbodorsal fascia and the dura ( Fig. 1 ) which makes it immobile and thus limits the upward movement of the conus medullarins during normal growth (this fact partially explains the deterioration in symptoms with increasing age,
physical effort,
degenerative changes ,and pregnancy) which consequently causes elongation and tethering of the spinal cord,
and is currently thought to explain the associated symptoms.
The spinal cord above the malformation is normal in appearance and position within the spinal canal.
Clinical manifestations:
Sphincter disorders are a recognised consequence of impaired innervation of the urinary system ,
they represent the most common complaint in suffers and the symptoms range from disorders of frequency,
continence,
and dysuria,
patients may also suffer from recurrent urinary tract infections.
Bowel dysfunction although rare is often associated with urinary disorders
Orthopaedic syndromes: Limb deformities ( Club foot (30%),high pedal arches,
hammer toes,
calcaneo-varus/valgus deformity),
Limb length discrepancy,
pain.
The Caudal Syndrome: described by Currarino in 1981 as a triad of anorectal,sacral and presacral anomalies,
linked to HLXB9 gene on chromosome 7.
Associated anomalies (Cord and Root Anomalies) the most common anomaly is terminal syringomyelia ( Fig. 2 ) but also includes dorsal,cervical and bulbar hydromyelia.
Other malformations do occur but present very infrequently.
Spinal Malformations: As a closed spinal dysraphism spina bifida is found in 69 to 89% of cases ,
the most common locations of the defect being L5 and sacral.
Other malformations such as sacral agenesis,
deformities of the longitudinal axis of the bony spine and other vertebral anomalies occur less frequently.
Brain Malformations: As mentioned before lipomyelomeningocele are not typically associated with Chiari or Dandy- Walker malformations.
Classification:
Lipomyelomeningocele was first classificated by Chapman into 3 categories according to the location of the lipoma and its relations with the neural components.
More recently a category was added by Pang to include the lesions that didn’t fit with the exsiting criteria.
This classification is merely neurosurgical and leaves out the correlation with radiological and clinical findings
Modified Chapman classification :
Described according to relationship of lipoma-cord interface into 3 subgroups:
- Dorsal
- Caudal or Terminal
-Transitional (Dorso caudal or Dorsolateral)
Recently- Chaotic lipoma
Characteristics of the different kind of lipomas :
Dorsal Lipoma
Located at a middle lumbar to lumbosacral level and proximal to the conus,
the lipoma is attached medially to the dorsal root entry,
which lies in the subarachnoid space.( Fig. 3 )
Caudal or Terminal lipoma
Originate at the conus medullaris or filum terminale,
the lipoma is located dorsal to the root entry,
the nerve roots are encompassed in the lipoma,
they are mostly intradural.
( Fig. 4 )
Transitional lipoma
A mix of the other two kind of lipomeningocoeles,more distal roots get entangled while the proximal ones tend to be spared ( Fig. 5 )
Chaotic lipoma:
Doesn’t have the characteristics of any other lipoma,
they start on the dorsal aspect and the distal portion is anterior to the placode,
all the neural tissue is involved in the lipoma which makes it impossible to separate the neural tissue.
Sacral agenesis is commonly associated.
( Fig. 6)
Radiological Assessment
Prenatal diagnosis: Look at the bony structure of the spine,
misplaced pockets of fat,
abnormalities in the distribution of spinal fluid or the length and morphology of the spinal cord.
A lot of subtle lesions go unnoticed
Plain Radiographs : Bony spina bifida,
vertebral agenesis,
sacrum abnormalities
Computed Tomography: mostly used to study the bony abnormalities.
Magnetic Resonance Imaging: Gold standard
It gives detailed information about the spinal cord and filum,
we should look at the level of the conus,
location of the lipoma,
and how it is related to the spinal cord,
if the spinal cord is rotated,
if it has other associated malformations,
how the roots relate to the lipoma and if the cord is mobile or not.
It allows 3D reconstructions which help the surgeon during surgical planning
MR imaging is not very good for post surgery follow up,
as scar tissue is very hard to differentiate from leftover fatty tissue from the lipomyelomeningocoele and it does not provide much information about the success of the surgery or if the spine has retethered.
Neurological Assessment
Necker functional score:
To appreciate the functional and social repercussions of these malformations,
and to allow rapid comparison between patients and appraise the evolution of the clinical symptoms,
the Necker functional scoring system was developed.
This score takes into account four handicaps: motor,
sensory,
Bladder and Bowel.
Normality is given a score of 5 for both motor and urinary function and 4 for sensory and anal sphincter function.
Asymptomatic patients have a score of 18 and a normal life is possible with a score above 15.
Score
|
Motor
|
Sensory
|
Bladder
|
Bowel
|
1
|
Wheelchair.
Major deficit*
|
Skin ulceration.
Amputation
|
Day and night incontinence
Incontinence*
|
Incontinence
|
2
|
Major orthesis.
Two crutches
|
Pain
|
Night incontinence.
Retention*
|
Painful constipation.
Digital maneuvers*
|
3
|
Distal orthesis
|
Painless deficit
|
Intermittent catheterization
|
Constipation
|
4
|
Fatigue on walking
|
Normal
|
Dysuria,Stress incontinence
|
Normal
|
5
|
Normal
|
|
Normal
|
|
*For children under the age of 3.