CT HEAD
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Featured
case Study 1
CT Head
Many thanks to
Grace Walker,
CT Superintendant, NHSL for her contribution to this case study.
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Clinical History
A 62-year-old female presented at the Accident and Emergency department with nausea and head and neck pain lasting more than a day. The patient was very difficult to assess because she was confused and disorientated.
On examination the patient had a reduced Glasgow Coma Scale (GCS) of 14/15, was hypertensive,180/90, had a bruise on her forehead over her right eye but had no cranial nerve deficits. She had some basal crackles in her chest.
Previous Medical History
She suffered from Crohn’s disease, angina, asthma and diabetes. She claimed to have been drinking the previous day.
A relative revealed that the patient had poor eyesight, was a non-insulin dependent diabetic and an ex-alcoholic who had been a member of Alcoholics Anonymous for six years. The patient lived alone and was normally independent and orientated.
Initial impressions were of an acute confusional state due to possible:
alcohol withdrawal
intracranial event
lower respiratory tract infection (LRTI
Tests
A chest x-ray excluded a LRTI and no vault fracture was detected on the skull
x-rays. Urinalysis revealed the presence of blood, ketones and protein. Blood tests revealed a decreased potassium level of 2.9 that was not classed as being significantly low. An increased white cell count level of 19.7 indicated a possible infection. All other results were within normal limits.
The clinical symptoms could indicate a subarachnoid haemorrhage (SAH), a stroke, meningitis or a cerebral abscess. The on-call radiologist agreed to carry out an emergency non-contrast computerised tomography (CT) brain scan. The scan would be reviewed and repeated with contrast enhancement if deemed necessary by the radiologist.
Technique
The departmental protocol for any emergency CT scan requires the patient to have patent venous access and to be accompanied by a trained member of staff, either medical or nursing, along with the patient's case notes. If it is required, intravenous contrast medium can be rapidly administered if the patient is already cannulated. This reduces the examination time for the patient and reduces delays in the CT department. It can be argued that patients who are ill enough to require an emergency CT scan should be cannulated anyway.
The patient was transferred to the CT department on a trolley, and although she seemed confused and agitated, she was able to properly identify herself according to departmental protocols and IR(ME)R regulations. The procedure was explained to the patient and she was reassured before she was transferred onto the scanner couch. She was positioned supine in the middle of the table with the median-sagital plane perpendicular to the couch top and her arms by her sides. Her head was placed in the headrest with the supra-orbital plane perpendicular to the couch top and inter-orbital plane parallel to the gantry. Because she was shaking considerably, restraining bands were used across her body and legs for immobilisation and patient safety. Foam wedges and velcro straps were also used to immobilise her head. It is departmental policy to use the supra-orbital baseline (SOBL) for CT brain scans and the patient's chin is normally tilted down towards the chest to exclude or reduce gantry angle to achieve this. Unfortunately this patient was unable to comply because of her neck discomfort.
Toshiba Aquillion 16 slice MDCT
PARAMETER VALUE
Topogram
Scan plan length 200 mm
Orientation Lateral
kV 120
mAs
Slice thickness 2 mm
Helical Scan
mAs 290
Rotation time 1 sec
Scan time 15 secs
Algorithm FC23
FC30
Slice acquisition 1 mm
Slice collimation 16 x 1 mm
Pitch 11 mm
Recon interval 0.8
Gantry angle 14.5
Scan field of view
(SFOV) 250 mm
Display field of view
(DFOV) 230 mm
Dose (DLP) 1.45Gycm
Images
The CT images are made up of a series of pixels. Each pixel has a CT number or Hounsfield Unit (HU) and is represented by a shade of grey. The HU represents the linear attenuation coefficient of the object imaged. There are 4096 values (-1024 - +3071) and 4,000 shades of grey. As the human eye can only see about 40 shades of grey, it is necessary to select the range to be viewed. This is called the Window Width (WW). A narrow width produces a high contrast image. The wider the WW the smoother the image but the image has less contrast and abnormalities could easily be missed, particularly small ones.
The Window Level (WL) is the central HU number of the range. Raising the WL darkens the image and lowering it brightens it.
Adjusting both of these factors allows the viewer to optimise the image data.
The brain should to be viewed on a narrow WW because there is only a slight difference in density between the grey and white matter. However, through the posterior fossa there is a much larger range in densities due to the petrous bones and so the WW should be increased.
Click Play to view images
Radiology Report
Unenhanced scan. There is a large high attenuation material with a fluid level overlying the convexity of the left parietal lobe consistent with acute on chronic subdural haematoma. This measures 3 cm in maximum depth. Further streaky areas of ill-defined high attenuation material is seen within the low density material overlying the convexity of both cerebral hemispheres; the appearance is suggestive of bilateral acute on chronic subdural haematoma. Although this extra axial collection is compressing both frontal and parietal lobes, there is no evidence of midline shift. The ventricles, basal cisterns and peripheral CSF spaces are still patent. Urgent neurosurgical review is recommended. Electronic images have been linked to neurological sciences for review. Findings discussed with the managing clinical team.
Conclusion
In this case study, no abnormality was detected on the skull images but this did not exclude intracranial damage. As the patient’s clinical condition continued to deteriorate, a possible stroke or haemorrhage was indicated.
CT is the preferred imaging modality for this type of case and the patient was scanned within 30mins of the request being received. The SOBL was selected for this patient as she had no facial or cervical spine injuries. Unfortunately she was unable to comply and the eyes were irradiated even with the gantry angled to its maximum for the table height. The CT excluded a skull fracture but demonstrated a SAH, due to a possible aneurysm. The patient was referred to a neurological institute and transferred within two hours of being scanned.
The CT scan had a direct impact on the patient management. It provided a definitive answer to the patient’s condition. As the scanning centre did not have the specialist treatment facilities the patient was quickly transferred to a centre where she was able to receive the appropriate specialised treatment.
We Hope you found this case study informative.
Why not try to reflect on this case study and the role of the radiographer in this urgent CT examination.
What type of preparation would be involved prior to the patient arriving?
Who would the radiographer need to communicate with within a multidisciplinary team?
What specialist skills, are required to carry out this type of scan?
These are just some questions that you could ask yourself when reflecting on a situation such as this.
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