Klippel-Feil Syndrome
The congenital abnormality characterized by absence or fusion of cervical vertebrae C1-C3 is Klippel-Feil syndrome (KFS). 1
Key Diagnostic Features
Klippel-Feil syndrome involves congenital fusion of two or more cervical vertebrae, which can include C1-C3, though the pattern and extent of fusion varies considerably between patients. 1, 2, 3
The condition presents with:
- Vertebral fusion (block vertebrae) visible on imaging 1
- Classic clinical triad (though not always present): short neck, low posterior hairline, and limited neck range of motion 2, 3
- Potential cervical spine instability, particularly at C1-C2 3
Associated Abnormalities
Patients with KFS frequently have additional congenital anomalies that significantly impact morbidity:
- Split cord malformations (SCM) and other neural tube defects 1
- Hemivertebrae, butterfly vertebrae, or additional fused vertebrae beyond the primary fusion 1
- Cervical spine instability affecting approximately 25% of skeletal dysplasias including KFS 4
- Spinal canal stenosis which can lead to myelopathy 1, 3
Diagnostic Approach
MRI is the preferred imaging modality for evaluating KFS and should be obtained in all suspected cases. 1 MRI provides:
- Detailed visualization of vertebral fusion patterns
- Assessment of spinal cord compression or myelopathy
- Identification of associated split cord malformations
- Evaluation of soft tissue and bone marrow abnormalities
Plain radiographs serve as complementary imaging to identify vertebral fusion, spondylosis, malalignment, or spinal canal stenosis. 1
Neurological examination must focus on signs of myelopathy (weakness, spasticity, hyperreflexia, gait disturbance) or radiculopathy (dermatomal sensory changes, focal weakness). 1
Critical Management Considerations
Airway management is a major concern in KFS patients requiring anesthesia due to limited neck mobility and difficult intubation. 4, 1 This is particularly important for:
- Surgical procedures requiring general anesthesia
- Pregnant women with KFS requiring delivery, who need specialized anesthetic planning 1
Avoid operative vaginal delivery when possible in patients with known or suspected skeletal dysplasias, as approximately 25% have C1-C2 instability that places the spinal cord at risk during delivery. 4
Important Clinical Pitfall
Do not confuse KFS with isolated posterior arch defects of C1, which are relatively common (4% prevalence) and usually asymptomatic. 5 Complete absence of the posterior arch of C1 without fusion to other vertebrae is extremely rare and represents a different entity than KFS. 5