What are the clinical indications for a CT?

CT examinations provide a great diagnostic and therapeutic added value in many areas of veterinary medicine. Within a very short examination time, we often receive groundbreaking information for further therapeutic and also prognostic steps.

→ Accurate diagnoses and simplified therapy planning are one of the greatest benefits of CT examinations.

What should be considered before the CT examination?

Before any further diagnostic examination, the patient should have a detailed medical history and clinical exam. Simpler and less expensive procedures such as blood tests or radiography should be considered if they can be diagnostically sufficient.

CT examinations should, if possible, be accompanied by a clear indication or question to perform target-oriented diagnostics and to limit the body area to be examined as much as possible. The larger the area examined, the more images and data volumes are generated, resulting in increased cost and time factors.
The benefit and therapeutic consequence of whole-body CT should be adequately weighed, since an enormous amount of data and cross-sectional images are generated, the evaluation of which requires a lot of time and costs; moreover, no animal should be anaesthetised unnecessarily.

Computed tomography is one of the most common imaging procedures, along with ultrasound and radiography. Each procedure has its own particular advantages as well as individual limitations. Often, an individual decision must be made as to which imaging is preferred; by no means all indications are to be considered absolute for a particular imaging procedure; frequently, they even complement each other.
If radiographs are sufficient or more suitable (e.g., gastric torsion or hip dysplasia in dogs), this modality of choice should be considered first.
However, decisions are often grey areas that require individual decisions as well as the necessary owner compliance. In numerous instances, the decision to perform a CT scan is made in relation to previous findings and depends on the question and other factors such as owner compliance and therapeutic consequences.
For example, while an abdominal ultrasound may be sufficient for diagnosis, in obese animals the use of a CT may be necessary because ultrasound does not achieve sufficient penetration depth.

Since anaesthesia and CT examinations in large animals are associated with greater effort, costs, and usually a higher risk of anaesthesia, the indication for a CT should be viewed particularly strictly here and should also be limited as precisely as possible.
Exceptions for anaesthesia are examinations of the head region in an equine patient, which can often be performed in a standing position on a sedated animal and is therefore associated with a lower risk for the patient. New technologies and modalities are evolving fast and provide the evaluation of other regions in a standing and sedated horse as well.

Example diagnosis of lameness in horses:

Before the decision for a CT examination is made, the following steps must be completed:

• Anamnesis and general examination
• Special lameness examination: palpation, provocation samples, assessment in motion, etc.
• Nerve block anaesthesia (if there is no risk of iatrogenic fracture)
• X-ray and ultrasound if necessary

If the results of these examinations remain questionable or without significant findings, using a CT or MRI scan is considered.

General indications for a computed tomographic examination

• For a reliable and complete diagnosis, in many cases a CT scan is the method of choice
• CT provides more detail, images are free of superimposition and available in 3D resolution, as well as increased soft tissue contrast when other imaging modalities reach their limits or provide questionable findings
• Chronic, recurrent symptomatology with unclear aetiology
• Areas that are difficult to access or require more detailed information (e.g. head area, complicated fractures, fissures, complex joints such as the carpal joint)
• Unclear localization of lameness despite detailed orthopaedic-neurological examination
• Early presentation of structural changes (e.g., examination for elbow dysplasia in dogs) → Clinical symptoms may be present at the very early stages of a disease, which, however, cannot yet be visualised in radiographs. In general, there is not always a correlation between clinical symptoms and imaging findings
• Determining the extent of damage or disease (prognosis and treatment decision)
• Tumour surgeries: preoperative metastasis screening (imaging of micrometastases)
• Surgeries: Decision-making and planning (e.g., extent of tumours, complexity of fractures, biopsies, or fine-needle aspiration)

Specific CT indications - an overview

Computed tomography is very commonly used to image bony structures including the spine and joints (e.g. Fragmented Coronoid Process FCP in dogs). Other primary applications include the thorax, abdomen, various head areas, vascular examinations, and the pelvic cavity with its organs.

Examples of common indications for a CT scan are:

• Polytrauma patients (craniocerebral trauma)
• Head region: fractures, tumours in the region of the skull, pathologies of the frontal and nasal cavities, the ears including inner ear, the jaw and teeth, orbital or retrobulbar processes (e.g. exophthalmos of unclear origin), pharynx, larynx, trachea, temporomandibular joint and masticatory apparatus
• Spine: fractures and dislocations, herniated or prolapsed discs, tumours, myelograms, etc.
• Joints: fissures, dislocations, joint dysplasias (especially canine elbow dysplasia)
• Bones: complex fractures
• Thorax: mediastinum, trachea, lungs, bronchi, pleura etc.
• Abdomen: liver, gallbladder and spleen, pancreas, gastrointestinal tract, urinary system (e.g. ectopic ureter), genital tract, adrenal glands, vascular and lymphatic collecting system
• Diagnosis and imaging of vascular anomalies (e.g. portosystemic shunt)
• Radiation planning in tumour patients
• …and many more

Limitations of computed tomography

CT is especially effective in imaging bony structures, but it sometimes reaches its limits in imaging of soft tissues, especially small soft tissues, even though the resolution is much better than conventional X-ray. In these cases, an ultrasound should complement the examination or an MRI if available.
MRI is considered the gold standard in examinations of the brain ; likewise, it is often preferred in neurodiagnostics and spine diseases. In practice, however, it must be mentioned that for reasons of cost, the considerably longer examination and thus anaesthesia duration, or simply due to lack of availability, a decision is often made in favour of CT examinations. Optimally performed and with sufficient knowledge of the limits, they can be sufficiently informative, for example, for the diagnosis of hydrocephalus, tumours, or haemorrhages.

The use of a CT not only facilitates and improves the diagnosis and therapy of patients. It can significantly improve the treatment spectrum and the reputation of your practice or clinic.

Do you need support?

DiploVets offers more than just diagnostics. We also understand us as a point of contact for questions and uncertainties that arise in connection with imaging and performance of CT scans.

Together we achieve the best diagnosis and treatment options.

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