A 9-year-old boy, who was known case of Morquio syndrome, presented with inability to hold neck and weakness of all four limbs. His previous whole spine screening MRI revealed spinal cord compression and myelomalacia at atlantoaxial level. CT evaluation of cervical spine was performed for surgical planning.
MRI T2-weighted whole spine screening (figure 1) revealed hypoplastic dens. Hypointense soft tissue thickening was seen around dens, indenting the spinal cord anteriorly. Posterior atlas arch indentation over cord was also noted. Resultant spinal cord compression and myelomalacia were seen at C1-C2 level. Anterior central beaking of vertebral bodies and enlargement of intervertebral discs were noted at multiple levels. Kyphotic deformity was seen at D11-D12 level. Pre-operative imaging with CT cervical spine bone window (figure 2) revealed hypoplastic dens, flattened vertebral bodies with central anterior beaking at multiple levels. Additionally, J-shaped sella was observed in this case. Soft tissue window (figure 3) revealed slightly hyperdense soft tissue thickening around vertebral bodies, including dens and within intervertebral discs. These spinal findings were typical of Morquio syndrome.
Background- Morquio syndrome, also called mucopolysaccharidoses (MPS) 4, is a rare autosomal recessive lysosomal storage disease. It has two types MPS 4A (OMIM-#253000) and MPS 4B (OMIM-#253010). Type A results from mutations in GALNS gene encoding for galactosamine-6-sulfate sulfatase and intracellular accumulation of keratan sulfate and chondroitin-6-sulfate. Whereas type B results from mutation in beta-galactosidase gene. The two types cannot be distinguished clinically. 
Clinical Perspective- It is clinically characterised by short trunk dwarfism, skeletal dysplasia, normal intelligence, and various non-skeletal systemic manifestations like corneal clouding, organomegaly and valve disease. Spinal abnormalities like odontoid hypoplasia, mucopolysaccharide deposits around vertebrae, ligamentous laxity with instability at C1-C2 level, and gibbus deformity in thoracic spine predispose to cord compression. This may lead to complications like paraplegia and quadriplegia. [1,2,3,4,5]
Imaging Perspective- Imaging plays a key role in diagnosis, presurgical assessment and postsurgical follow up.
Key spinal findings for diagnosis of MPS 4 are small dens, dural and synovial thickening around C1-C2 with ligamentous laxity and indention by posterior atlas arch causing cord compression. Flexion-extension views may be required to demonstrate laxity of transverse odontoid ligament. Reduced vertebral height and central beaking of vertebral bodies are seen. Other typical findings are gibbus deformity at thoracic spine and abnormally enlarged intervertebral discs. [2,3,4,5,6,7]
Detailed evaluation with CT/MRI is needed in presurgical assessment. Demonstration of level and degree of bony spinal canal narrowing, compressive myelopathy changes, and vascular anatomy, especially vertebral artery course are important for surgical planning. Post-surgical follow-up imaging is needed to assess surgical complications and to confirm position of surgical implants. [8,9]
Outcome- Affected individuals have short life span of two to three decades. Symptomatic treatment plays an important role in management. Neurosurgical intervention is directed towards release of spinal cord compression and to improve atlantoaxial stability. Neurosurgical options include posterior occipito-cervical fixation and atlantoaxial arthrodesis. [8,9,10,11] Enzyme replacement therapy is also being developed for the condition. Elosulfase alpha has been approved recently for MPS 4A. 
Take-Home Message / Teaching Points- As spine involvement is a predominant feature of Morquio syndrome, awareness of the unique constellation of imaging findings is important. Assessment of level and severity of cord compression is a crucial step in management.
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