Review of Neck CT Studies Without CNS Windows Can Miss Crucial Spinal Cord Findings Jonathan G. Murnick, MD, PhD Children’s National Health System Washington, DC Presentation #1915

Disclosures None. 2

CT Image Contrast 3 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 TissueHU Bone500 Air-1000 Muscle70 IV Contrast (intravascular) 250 Fat-80 CSF10 Spinal cord50

CT Image Contrast 4 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 TissueHU Bone500 Air-1000 Muscle70 IV Contrast (intravascular) 250 Fat-80 CSF10 Spinal cord50

Normal Neck CT 5 Bone windows Soft tissue windows

Using CNS Windows 6 Contrast between spinal cord and CSF is poor on both bone and soft tissue windows Soft tissue windows Bone windows

Using CNS Windows 7 CNS windows dramatically improve contrast in the spinal canal Soft tissue windows Bone windows CNS windows

CNS Windows 8 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

Case #1: Neck Pain after Fall 9 An 8-year-old girl presented to the ED with neck pain after a fall during gymnastics Cervical spine CT was performed

Case #1: Neck Pain after Fall 10 No fracture was identified, and the patient was discharged home. Bone windows Soft tissue windows

Case #1: Neck Pain after Fall 11 Review in CSF windows (not performed at time of interpretation) shows expansion of the cervical spinal cord, with loss of surrounding subarachnoid space

Case #1: Neck Pain after Fall 12 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

Case #2: Neck pain and stiffness 13 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

Case #2: Neck pain and stiffness 14 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

Case #2: Neck pain and stiffness 15 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

Case #2: Neck pain and stiffness 16 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

Case #2: Neck pain and stiffness 17 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

Case #3: Jaw pain and trismus 18 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

Case #3: Jaw pain and trismus 19 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

Case #3: Jaw pain and trismus 20 Review in CNS windows (not performed at time of interpretation) shows a large cervical cord syrinx

Case #3: Jaw pain and trismus 21 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

Case #3: Jaw pain and trismus 22 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

Summary Points 23 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

References 24 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: Seo J-H, et al. “Severe spastic trismus without generalized spasticity after unilateral brain stem stroke.” Ann Rehabil Med (2012) 36: Jelasic F & Freitak V. “Inverse activity of masticatory muscles with and without trismus: a brainstem syndrome.” J Neurol Neurosurg Psych (1978) 41: