Review of Neck CT Studies Without CNS Windows Can Miss Crucial Spinal Cord Findings

Jonathan G. Murnick, MD, PhDChildren’s National Health SystemWashington, DCPresentation #1915

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Disclosures

None.

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CT Image Contrast

• CT viewing windows are chosen to maximize image contrast

• Table shows approximate Hounsfield unit (HU) values for different types of tissue found in the neck on a contrast-enhanced CT

Tissue HU

Bone 500

Air -1000

Muscle 70

IV Contrast (intravascular)

250

Fat -80

CSF 10

Spinal cord 50

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CT Image Contrast

• A neck CT is typically viewed using two different sets of windows: “bone windows” and “soft tissue windows”

• Bone windows• Center ~400; Width ~2000• Optimize visualization of bone

• Soft tissue windows• Center ~50; Width ~400• Optimize soft tissue contrast,

including vessels, muscle, lymph nodes, fat

Tissue HU

Bone 500

Air -1000

Muscle 70

IV Contrast (intravascular)

250

Fat -80

CSF 10

Spinal cord 50

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Normal Neck CT

Bone windows Soft tissue windows

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Using CNS Windows

• Contrast between spinal cord and CSF is poor on both bone and soft tissue windows

Soft tissue windowsBone windows

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Using CNS Windows

• CNS windows dramatically improve contrast in the spinal canal

Soft tissue windowsBone windows

CNS windows

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CNS Windows

• CNS windows are typically used to view intracranial structures

• Easy to differentiate brain parenchyma from CSF

• Show intracranial hemorrhage• When used in the neck, these

windows differentiate spinal cord from CSF

• Following are three missed cases where CNS windows demonstrate important pathology

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Case #1: Neck Pain after Fall

• An 8-year-old girl presented to the ED with neck pain after a fall during gymnastics

• Cervical spine CT was performed

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Case #1: Neck Pain after Fall

• No fracture was identified, and the patient was discharged home.

Bone windows

Soft tissue windows

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Case #1: Neck Pain after Fall

• Review in CSF windows (not performed at time of interpretation) shows expansion of the cervical spinal cord, with loss of surrounding subarachnoid space

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Case #1: Neck Pain after Fall

• 4 days later, the patient again presented to the ED with new symptoms of left arm weakness

• The patient was admitted, and MRI showed an expansile mass lesion in the cervical cord

• Biopsy was consistent with GBM

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Case #2: Neck pain and stiffness

• An 18-month-old girl presented to the ED with 5 days of sore throat, cough, neck pain, and neck stiffness

• Contrast-enhanced CT of the neck was performed

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Case #2: Neck pain and stiffness

• CT of the neck was read as notable for mild tonsillar and retropharyngeal edema; no abscess identified

• The patient was admitted to the hospital for antibiotics for presumed tonsillitis

Soft tissue windows

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Case #2: Neck pain and stiffness

• 6 hours later, the CT was re-reviewed in CNS windows

• A hyperdense spinal epidural lesion was identified, with severe mass effect on the cord

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Case #2: Neck pain and stiffness

• MRI was consistent with an epidural hematoma at the cervicothoracic junction; no mass lesion or vascular malformation was seen

• Bland hematoma was evacuated at surgery

• The patient is well, with no neurologic sequela

T1 precontrast

FSEIR

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Case #2: Neck pain and stiffness

• Spontaneous spinal epidural hematoma is a rare but known cause of spinal cord compression in young children

• Most commonly at the cervicothoracic junction

• Hypothesized to result when an epidural vein ruptures due to transiently raised intrathoracic pressure. (Note that this patient had a history of cough.)

T1 precontrast

FSEIR

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Case #3: Jaw pain and trismus

• A 3-year-old boy presented to oral surgery clinic with 4 weeks of jaw pain and trismus (inability to open the mouth)

• CT of the face was ordered

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Case #3: Jaw pain and trismus

• Nonspecific periosteal reaction was noted of the right mandibular condyle

• Study was read as otherwise normal• Note that no abnormality is readily apparent in the spinal canal

on soft tissue windows

Bone windows

Soft tissue windows

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Case #3: Jaw pain and trismus

• Review in CNS windows (not performed at time of interpretation) shows a large cervical cord syrinx

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Case #3: Jaw pain and trismus

• 5 days later, the patient was admitted to the hospital for optimization of nutrition (he had lost 11 pounds due to trismus) and further workup

• MRI of the brain showed a Chiari 1 malformation, with a large syrinx dissecting upward into the brainstem (syringobulbia)

• The patient underwent Chiari decompression surgery with near-complete resolution of the syrinx and substantial improvement in symptoms of trismus

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Case #3: Jaw pain and trismus

• Syrinx likely led to trismus by affecting the trigemenal motor nucleus in the dorsal pons

• Trismus secondary to injury to the dorsal pons has been previously reported in cases of stroke, trauma, and tumor

www.neuroanatomy.wisc.edu/virtualbrain

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Summary Points

• CT scans of the neck, face, and cervical spine all include portions of the spinal canal in the imaged volume, even if it is not the primary focus of the study

• It is important to review the spinal canal in windows optimized for CNS structures; otherwise, key findings can be missed

• Although unusual, syringobulbia can present as trismus

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References

Schoonjans A-S, et al. “Spontaneous spinal epidural hematoma in infancy: Review of the literature and the “seventh” case report.” Eur J Paediatr Neurol (2013) 17: 537-542.

Seo J-H, et al. “Severe spastic trismus without generalized spasticity after unilateral brain stem stroke.” Ann Rehabil Med (2012) 36: 154-158

Jelasic F & Freitak V. “Inverse activity of masticatory muscles with and without trismus: a brainstem syndrome.” J Neurol Neurosurg Psych (1978) 41: 798-804