Craniovertebral Congenital Anomalies & Variants

Question 1

What line is used to diagnose basilar impression with occipitalization?

Answer 1

McGregor’s line
(Dens >8-10mm above)

Question 2

Name 4 possible causes of primary basilar impression

Answer 2

• occipitalization of atlas
• agenesis/hypoplasia of atlas
• Klippel Feil syndrome
• chiari malformation

Question 3

Name 4 possible causes of secondary basilar impression

Answer 3

• pagets
• osteomalacia
• fibrous dysplasia
• osteogenesis imperfecta

Question 4

What is occipitalization?

Answer 4

Congenital fusion of C0/C1

Question 5

What are the radiographic findings of occipitalization?

Answer 5

• may appear as no C1, but C1 agenesis doesn’t exist
• lat: decreased jt space, no spinolaminar line
• APOM: no visible jt between C0/C1

Question 6

What is the clinical significance of occipitalization?

Answer 6

Concern for atlantoaxial instability

Question 7

What is occipitalization frequently associated with?

Answer 7

• C2/C3 fusion
• skull base morphology (basilar impression)

Question 8

What are your next steps for a patient who is occipitalized?

Answer 8

• flexion/extension radiographs to check for instability (can have acquired or congenital problem w/ transverse lig)
• thorough neuro exam
• advanced imaging

Question 9

What is a chiari malformation?

Answer 9

Herniation of the cerebellum more than 5mm beyond the margin of the foramen magnum

Question 10

What is the clinical significance of a chiari malformation?

Answer 10

Can cause hydrocephalus if foramen of magendie and Luschka (4th ventricle drainage sites) are clogged

Question 11

What other anomaly is associated with chiari malformations?

Answer 11

syrinx/syringomyelia

Question 12

What is a syrinx?

Answer 12

Fluid-filled cyst in central aqueduct/spinal cord

Question 13

What is syringomyelia?

Answer 13

When a syrinx causes neurological symptoms

Question 14

What anatomical region is most commonly affected by syringomyelia?

Answer 14

Upper extremity

Question 15

What are the radiographic findings of a chiari malformation?

Answer 15

Plain radiographs are typically not helpful with diagnosis, but may show associated skeletal malformations (eg. Occipitalization)

Question 16

How is a chiari malformation diagnosed?

Answer 16

MRI
- herniation of cerebellum >5mm beyond foramen magnum
- cerebellar tonsils appear peg-shaped, elongated, and low-lying

Question 17

What are your next steps if a chiari malformation is found?

Answer 17

• neuro consult to R/o other findings (may need surgery)
• brain MRI

Question 18

What are the symptoms of a chiari malformation?

Answer 18

May be clinically silent with no symptoms
- headache (MC)
- cervical/facial pain

Question 19

Your patient who is occipitalized shows positive results on neurological examination. After obtaining flexion/extension radiographs, what are your next steps?

Answer 19

order MRI to check for Chiari malformation

Question 20

How is a syrinx diagnosed?

Answer 20

T/S MRI
Appears as bright streak

Question 21

What are the possible symptoms of syringomyelia?

Answer 21

Neuropathic arthritis
- cloak-like pain (neck & shoulder area)
- loss of pain and temperature sensation

Question 22

What is the most common anomaly of the craniovertebral junction?

Answer 22

Occipitalization

Question 23

What is an epitransverse process?

Answer 23

A variation of congenital bone bar that extends from the atlas TP, superiorly toward the adjacent occiput
(may form a joint or fuse)

Question 24

What is the diagnosis?

Answer 24

Epitransverse process

Question 25

What is a paracondylar process?

Answer 25

A variation of congenital bone bar that extends more medial and anterior to the paracondylar area of the occiput
(may form a joint or fuse)

Question 26

What is the diagnosis?

Answer 26

Paracondylar process (arrow)
(Arrowhead = styloid process)

Question 27

What is the most common form of an occipital vertebrae?

Answer 27

third condyle

Question 28

What is a third condyle?

Answer 28

midline bony process located between the 2 occipital condyles and continuous with the anterior foramen magnum

Question 29

What is the diagnosis?

Answer 29

Third condyle
(Not visible on APOM)