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|LETTER TO EDITOR
|Year : 2015 | Volume
| Issue : 1 | Page : 122-123
Spinal lipoma with tibial hemimelia-incidental or causative? Revisiting the McCredie-McBride hypothesis
Prasad Krishnan1, Sutirtha Chakraborty2
1 Department of Neurosurgery, National Neurosciences Centre, Calcutta, West Bengal, India
2 Peerless Hospital and B. K Roy Research Centre, Calcutta, West Bengal, India
|Date of Web Publication||4-Mar-2015|
Department of Neurosurgery, National Neurosciences Centre, Calcutta, West Bengal
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Krishnan P, Chakraborty S. Spinal lipoma with tibial hemimelia-incidental or causative? Revisiting the McCredie-McBride hypothesis. Neurol India 2015;63:122-3
A 32-year-old female with congenitally short left lower limb [Figure 1] who was able to independently ambulate with a crutch presented to the Department of Orthopedics for lower limb prosthesis. Her radiographs revealed a Type-1 left tibial hemimelia and a dysplastic femur with a poorly developed femoral head and acetabulum [Figure 2]. Hence, a custom-made lower limb prosthesis with a pelvic support was planned. On examination, it was found that there was a tuft of hair in her lower back [Figure 1] for which a neurosurgical opinion was sought. On examination, she was continent with no sphincteric dysfunction. The power was normal in the right lower limb with normal reflexes. The left lower limb was flail although some movement was present at all joints. There was no sensory deficit in the limbs or in the perianal region. There was a varus deformity of the foot [Figure 1]. X-rays of the lumbosacral (LS) spine showed multilevel spina bifida [Figure 2]. Magnetic resonance imaging (MRI) of the LS spine showed an intraspinal lipoma at D11 to L1 levels [Figure 3]. This was present more on the left side and the cord too was thinned out on the left side [Figure 3]. The ultrasound abdomen revealed normal kidneys and bladder with no evidence of residual post-void urine. No surgery was performed but her family was counseled about the possibility of neurological deterioration in the future and the patient was told to review periodically in the Neurosurgery Department.
|Figure 1: Clinical photograph of the patient showing (a) shortened left lower limb with varus deformity of foot and (b) tuft of hair in the lower back on the left side|
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|Figure 2: X-rays showing (a) complete agenesis of left tibia with deformed, shortened femur, (b) dysplastic femoral head, and acetabulum with poorly formed ilium, and (c) spina bifida in the lumbar spine|
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|Figure 3: Magnetic resonance imaging showing (a) a lipoma extending from D11 to L1 levels on sagittal T1 images, (b) the lipoma is present posteriorly and to the left compressing the cord anteriorly and to the right on axial T1 images, and (c) thinned cord on the left side in coronal T2 images|
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Tibial hemimelia is a rare congenital abnormality with an incidence of one in 1,000,000 live births.  It can be of four types  -with a complete absence of the tibia, as in our case, being classified as Type-1. While it can be associated with several other congenital abnormalities, the commonest spinal problem reported with dysmelia is scoliosis.  We encountered one report describing its association with hemivertebrae  and the other with a spinal lipoma. 
The influence of the development of the neural crest on limb morphogenesis came to light in experimental studies in the wake of the thalidomide disaster where it was noticed that ultrastructural changes predating the development of limb formation appeared in those dorsal root ganglia and their neurons that corresponded to the deformed limb segments. , This theory of "embryonic sensory neuropathy"  contributing to the genesis of dysmelia is called the McCredie-McBride hypothesis.
The vital question in our case was whether the lipoma had contributed to the dysmelia by interfering with the functions of the dorsal horn cells; or, was it an incidental finding? It is worth noting that the side of the limb deformity and the side of the lipoma were the same (i.e., the left side). Moreover, the lipoma was posteriorly placed, i.e., in the region where the dorsal columns of the spinal cord should have been present and the MRI also showed asymmetrical cord atrophy (more on the left side). Furthermore, the location of the lipoma at D11 to L1 vertebral segments on the left side corresponded to the cord segments innervating the dysmelic lower limb.
However, the incidence of spinal lipoma is far more common (1 in 4,000 patients)  than that of hemimelia; and, while spinal lipomas may cause tethering or pressure effect on the cord, they have not been reported to completely replace the neural tissue or cause gross agenesis of the nerves. In fact, the cord-lipoma junction is said to be medial to the dorsal root entry zone.  Hence, an explanation of lipoma-induced dysgenesis of posterior columns leading to dysmelia may not be tenable (unlike in cases with thalidomide toxicity) and their association, in this case, may merely be a random occurrence of two unrelated congenital abnormalities.
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[Figure 1], [Figure 2], [Figure 3]