common pathology in post contrast head and neck ct

head and face

orbital cellulitus

Orbital cellulitis is an emergency with serious complications including intracranial infection, cavernous sinus thrombosis and vision loss. Urgent imaging and surgical consultation (ENT and ophthalmology) should be considered for any child with suspected orbital cellulitis

Periorbital and orbital cellulitis are distinct clinical diseases, though have overlapping clinical features and therefore can be difficult to differentiate

Orbital cellulitis: infection within the orbit

- surgical emergency with major complications including loss of vision, abscess formation, venous sinus thrombosis and extension to intracranial infection with subdural empyema, and meningitis

Periorbital cellulitis: infection of the eye lids and surrounding skin not involving the orbit

Often managed with IV antibiotics

The globe is not involved in either infection

It is often imaged with CT and can appear as the following;

poor definition of orbital planes
inflammatory stranding in the intraconal fat
intraconal or extraconal soft tissue mass
oedema of the extraocular muscles
intraorbital abscess
subperiosteal abscess (1) (2)

Protocol for orbital cellulitus: Force CT-CP-102 Orbital Cellulitis and Mastoiditis. 2023. Under review.docx

Main points to note from protocol

60 seconds post IV contrast
Whole orbits and brain is included in case of intracranial extension

Case studies for orbital cellutius: Compare both eyes and sinus in images to try and spot the differences

4 year old with L eye and face swelling

Radiologist report:

Diffuse pansinusitis with a left orbital cellulitis and a left subperiosteal collection. The left subperiosteal collection is contiguous with likely pus within the left ethmoid, maxillary sinuses which extends all along the medial border of the maxilla and nasal bone anteriorly. There is associated expansion and thinning of the osteomeatal complex and cortical breach/thinning of the medial, anterior wall of the left maxillary sinus and left lamina papyracea. No evidence of intracranial extension

21 MONTH OLD WITH PROGRESSIVE LEFT OBRITAL CELLUTIUS

Radiologist report:

There is evidence of worsening left orbital cellulitis, with an increasing volume subperiosteal collection/abscess subjacent to the left lamina papyracea. There is apparent extension via the nasolacrimal duct into the nasal cavity, with an increasing volume rim enhancing collection in the anterior left nasal cavity. There is diffuse thinning /rarefaction of the medial bony wall of both the maxillary sinus and left orbit, with several more discrete bone defects identified. There is evidence of accompanying acute sinus disease with progressive and complete opacification of the left maxillary sinus with complex fluid, air fluid level in the right maxillary sinus and partial opacification of the remaining pneumatised left mastoid air cells and middle ear cavity. There Is no CT evidence of secondary intracranial complication.

Cases from RCH

cerebral venoUS SINUS THROMBOSIS

The occlusion of the venous system in the brain due to venous clots. Can occur from multiple factors including but not limited to the following

dehydration
systematic illness
trauma
infection
metastases
hormonal changes

On CT is appears as hyperdensity in venous sinuses. Post contrast it can appear as a filling defect. It can also be associated with hemorrhage or infarction due to venous hypertension. (4)

Protocol for a venogram: Force CT-CP-103 CTV head CT 2024.docx

Main points from protocol: 45s post contrast (maximum 50mls)

Above image: Non-contrast brain with 2 x hyperdensities in the superior sagittal sinuses

Below image: Venogram (post contrast brain) with 2 x Filling defect in the superior sagittal sinus (4)

Both cases from Radiopedia (3)

post contrast head

Contrast is also used in brains to assess for space occupying lesions and absesses. This is rarley done at RCH as most of these patients will receive MRI's..

C+ Brain protocol: Force CT-CP-101 Brain. 2024.docx

Tips for scanning: The delay for a post contrast brain is 2-4 minutes. The length of delay is dictated by the radiologists. This is the only scan we can routinely use a hand injection. You can also use the power injector at low rate (0.8-1.0ml/s)

Abysses will often appear as rim enhancing with cystic/hypodense centres (Left)

On pre-contrast imaging, SOL's may be isodense, hypodense or hyperdense compared to normal brain parenchyma with variable amounts of surrounding oedema. Following administration of contrast, enhancement is also variable and can be intense, punctate, nodular or ring-enhancing. (Right images. C- above, C+ below) (3)

neck

retro pharangeal abcyss

Retropharyngeal abscesses are most frequently encountered in children, with 75% of cases occurring before the age of 5 years, and often in the first year of life. This is likely due to the combination of prominent retropharyngeal nodal tissue and frequency of middle ear and nasopharyngeal infections. Retropharyngeal abscesses are thought to result as a complication of a primary infection elsewhere in the head and neck including the nasopharynx, paranasal sinuses, or middle ear

Symptoms include drooling, fever, neck swelling and limited range of motion and stridor

It is an important diseases to diagnose as it could lead o further infection or narrowing of the airways/vessels of the neck. (5)

On CT it can appear as;

Hypodense lesion +/- rim enhancement
Soft tissue swelling
Mass effect

Left above: Extensive retropharyngeal abysses resulting in airway impairment (5)

Left below: Free fluid in the retropharyngeal space. RCH case

Below: Compartments of the neck (5)

soft tissue neck protocol

An ideal soft tissue neck scan will have the following;

Enhancement of arteries ( Internal Carotid = red, Vertebral = blue)
Enhancement of veins (Jugular = Yellow)
Enhancement of any soft tissue infection (this could take up to 2 minutes to enhance)

To obtain imaging in both places we perform a split bolus technique ( 2 contrast injections and 1 scan) with a large delay between injections

Force CT-CP-203 CT Soft tissue neck. 2023. Under review.docx

Eg 10kg patient = 15mls contrast total (1.5ml/kg). For scan the following contrast would be given;

- 5mls given (1/3rd of 15mls)
- 2 minute delay
- 10mls given (2/3rd of 15mls)
- Scan 5 seconds post this ending

References

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