Imaging

Your pet is about to have an ultrasound?

Ultrasonography is a diagnostic procedure meant to investigate the source of your animal’s clinical signs, or symptoms. A conclusive diagnosis may be reached in several patients. However, as for any other diagnostic test, it may only represent one of the necessary steps to reach a confident diagnosis. While it may not always allow a final diagnosis, it greatly helps in ruling out some of the initial diagnostic differentials, or hypotheses. Sonographic findings are often used to better identify the next step to reach a final conclusion or to determine optimal treatment.

Why ultrasonography?

The principal strength of ultrasonography is its capacity to assess the size, shape and inner structure of tissues other than lungs and bones. Ultrasonography allows to assess tissue malformations (ex. congenital anomaly), tissue infiltrations (ex. cancer), obstructions (ex. ingested foreign body or urinary calculi), and inflammation (ex. pancreatitis). It also allows with Doppler to assess vessels for abnormal shunting or thrombosis. Ultrasonography is thus the ideal diagnostic modality for abdominal organs, heart, muscles and tendons, thyroid glands, and for soft tissue masses in most body parts.

Ultrasonography has its limitation

Ultrasound waves travel well in uniform soft tissue and liquid media, but cannot penetrate gas or mineral structures. Ultrasonography is therefore not useful for assessing bones or soft tissues surrounded with bone such as the spinal cord, unless there is demineralization. Aerated structures such as lungs are also inaccessible with ultrasound unless gas is replaced by soft tissues or fluid (such as for a superficial lung mass). A gas-filled gastrointestinal tract also limits the propagation of ultrasound waves.

While ultrasonography is great for the detection of nodules, masses or other lesions in an organ, it may not allow to differenciate benign from malignant lesions. An organ may also be diffusely affected without detectable sonographic changes, or with changes that may not be specific to a single pathology. In such instances, fine-needle aspirations or biopsies may be required to confirm the diagnosis.

Fine-needle aspirations

FNA is a simple procedure that is routinely performed in our hospitals. A fine needle – the same used for blood samples – is inserted into the abnormal organ or structure to obtain a sample for cytological evaluation. Slides with these samples are then submitted to clinical pathologist and results are typically available within 48 hours. In rare instances (< 5% of patients), FNA may provoke bleeding that is most often self-limiting, or rarely necessitate special treatments. For patients at risk, precautionary measures (i.e. hematology and coagulation tests) may be recommended prior to the procedure. A sedation may be used for more sensitive or anxious patients to minimize their stress and prevent movement during the puncture. In general, this procedure is well tolerated, causing a discomfort similar to regular blood punctures. This procedure is only recommended when its diagnostic benefit greatly surpasses its risk for the patient.

Patient preparation

For an optimized ultrasound exam, patients must be well prepared :

Stage 1. Animals must be fasted to limit the accumulation of food and gas that can significantly hamper the assessment of profound parts of the abdomen. Normal structures may be misinterpreted as abnormal and real lesions may be missed.

Stage 2. The hair over the region to be examined must be clipped and cleaned to allow good contact between the probe and the skin, a prerequisite for optimal ultrasound wave propagation. Images are otherwise degraded, which limits diagnosis.

Stage 3. A gentle restrain by trained technicians is usually sufficient for the examination. However, a light sedation may be necessary for some nervous patients for complete abdominal examination or for fine-needle aspirations.

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