The radiographic examination of the ferret is easily performed and can provide important information even though the technique has some limitations, which should be considered. The interpretation of X-rays of a ferret has much in common with the radiographic examination of dogs and cats, together with peculiarities typical of the species.
In view of the small size of the animal and the frequent presence of disorders not immediately evident at physical examination, it is always preferable to use big radiographic cassettes on which to perform simultaneously both the lateral (LL) and the ventrodorsal (VD) views. For more specific examinations, mammography films and cassettes can be successfully used as well. Due to its small size, the ferret should be placed directly on the radiographic cassette, without using a grid.
The standard lateral view is with the animal in right lateral recumbency. The limbs can be left as they are, or hyperextended. Radiographs of the head usually require a dorsoventral (DV) view; a VD view is also possible even though, in this case, the head should be immobilized with tape at the level of the chin, in order to keep it extended. The lateral view of the head can be obtained with the animal’s mouth either closed or open (thislatter view allows a better assessment of dentition). Rostrocaudal and oblique views of the head are not routinely performed; they can however be used for specific indications.
A proper interpretation of radiographic images inevitably requires correct positioning;it is therefore better to perform X-rays on sedated subjects. The fastest, safest and most practical solution consists in performing a short anaesthesia with isoflurane, with direct induction through a mask. In very docile or debilitated subjects, and if the operator is fast with the manoeuvre, X-rays can be taken with the animal awake. By holding the ferretby the scruff of its neck it is possible to rapidly immobilizeit for both a lateral and a ventrodorsal view; an acceptable position can be obtained by gently pulling the animal’s hind limbs. In order to examine the thorax, the front limbs should be extended in such a way as to avoid any overlapping with the thoracic organs.
THORAX
Radiography is a very good technique to assess intra-thoracic structures and in particular alterationsin the lung tissue and in the cardiac silhouette. The thorax of the ferret differs considerably from that of dogs and cats (Figs. 1 and 2). In relation to body volume, the thoracic surface area is relatively voluminous and elongated in shape, with the heart in a posterior position; in lateral views the thorax is positioned between the sixth and the eighth rib. The normal shape of a ferret’s heart is relatively more roundedthan that of a dog or cat. A specificity of this species is that the heart can be slightly raisedfrom the sternum, due to the interposition of adipose tissue between the sternum and the cardiac apex, an anatomical feature not to be confused with a pneumothorax.
The radiographic interpretation of the more common heart, pulmonary, infective and neoplastic disorders is similar to that carried out in the cat. Pulmonary infections may present as interstitial and alveolar infiltrations, which may overlap with the cardiac silhouette and obscure it (Figs. 3 and 4). Heart diseases (Fig. 5) are characterized by dorsal deviation of the trachea, increased heart surface area, pleural effusion, pulmonary congestion, decreased space between the rear margin of the heart and the diaphragm. In the differential diagnosis it is also worth mentioning that intra-thoracic neoplasms, by displacing the heart, can deviate the trachea dorsally (Fig. 6). An enlarged cardiac silhouette can be caused by cardiomegaly or, more rarely, by neoplasms or pleural effusion. Whenever an altered heart profile is identified on X-rays the appropriate diagnostic protocol should include an echocardiogram.
Thoracic neoplasms (for the most part lymphomas; Figs. 7-9) are mainly localized in the front part of the mediastinum, but they can also involve the pulmonary parenchyma and be the cause of thoracic effusion. Pleural effusion is evidenced by a generalized increase in thoracic opacity, which obscures its structures (Figs. 10 and 11). In the less severe forms the caudal pulmonary lobes, surrounded by fluid, are still evident. Possible causes of effusion are intra-thoracic neoplasms, cardiopulmonary filariosis, heart failure and haemothorax.
Megaoesophagus is a rare condition; the oesophagus appears full of air or food and the VD view can show a deviation of the trachea to the right. The administration of barium allows a better view of the structure. The presence of pneumomediastinum causes a dorsal displacement of the heart, which moves away from the sternum, and can be accompanied bythe collapse of one or more pulmonary lobes or by bone fractures. A diaphragmatic hernia can be the consequence of trauma and its radiographic presentation is similar to that of the cat (Fig. 12).
ABDOMEN
The abdominal organs which are usually assessed radiographically are the liver, stomach, kidneys, spleen, bowel loops and the bladder, when full (Figs. 13 and 14).
The spleen can be considerably increased in volume, especially in old and mature ferrets, to the extent of invading the right half of the abdominal cavity, but this is usually of no pathological significance. An increase in spleen volume may be the result of verydifferent pathologies: respiratory infections, heartor gastrointestinal diseases, insulinoma, adrenal disease, aleutian disease. In these cases the cytology is usually indicative of extramedullary hematopoiesis (Fig. 15). Primary diseases are rare, and usually consist in abscesses, torsions, mycobacterial infections, neoplasms, hypersplenism. Gas anaesthesia, after a few minutes, causes an increase in spleen volume, because of erythrocyte sequestration. In the presence of splenomegaly, a needle aspirate may potentially allow to differentiate between physiological and pathological conditions.
The stomach can appear more or less distended, depending on the amount of food present, but generally it does not contain gas. The amount of gas normally present in the intestine is very low; the presence of gas-distended loops should make one strongly suspicious of a foreign body obstruction or, less commonly, of ileus. Unfortunately, the radiographic differentiation between the two pathological conditions is not simple. In the presence of a foreign body obstruction, the stomach may also expand due to the presence of air (Figs. 16 and 17). An increase in intestinal gas is often accompanied by intestinal infections. Gastrointestinal foreign bodies are quite common: they usually consist of rubber, plastic and other radiolucent materials which are thereforenot visible radiographically; signs of obstruction, such as gas-dilated loops, are however identifiable.
The cranial pole of the right kidney is located at the level of T14,and that of the left kidney at L1. Their dorsal surface is in direct contact with the sublumbar muscles. Stones of the urinary tract are rare, but if present they can be identified because of their radio-opacity (Fig. 18). A distention of the bladder, in the absence of stones, can be the consequence of prostatic hypertrophy secondary to adrenal disease. A prostate increased in volume or prostatic cysts secondary to adrenal disease may sometimes be seen radiographically.
Normal adrenal glands cannot be identified radiographically and usually nor canpathological adrenal glands, unless they are significantly increased in volume. Insulinomas are also not detectable radiographically.
Mediastinal lymph nodes can be evident if they are significantly increased in volume due to the presence of infectious or neoplastic processes.
In the ferret, ascites is relatively rare (Figs. 19-21). If present, the intestinal content cannot be distinguished (with the possible exceptionof intestinal gas) and the abdomen is uniformly radio-opaque. The main causes of ascites are heart failure and neoplasms (especially lymphoma), more rarely hypoproteinaemia, liver and kidneys diseases.
Contrast medium
The use of contrast medium in the study of the gastrointestinal system of the ferret does not have many indications. The main indication is for diagnosing megaoesophagus, in any casequite a rare condition. The contrast medium generally used is barium sulfate (10-15 ml/kg), after fasting for 4-5 hours, to be administered preferably orally in the conscious ferret; in order to make the substance more palatable it can be mixed, for example, with a meat-based homogenized food. The administration by means of a gastric tube requires sedation, but it carries the risk of gastric reflux and subsequent aspiration. If an intestinal perforation is suspected the use of barium should be avoided and an iodinated contrast medium suitable for intravenous administration should be used instead. X-rays are taken immediately after the administration of the contrast medium and again after 20 and 40 minutes. Gastric emptying starts immediately; the contrast medium reaches the colon in less than 2 hours. The thickness of the small intestine does not normally exceed 5-7 mm.
SKELETON
The skeletal elements of the ferret are the same as those of dogs and cats. Worth noting is the presence of the baculum (os penis), long and thin and with a slightly J-shaped curved tip (see Fig. 18).
Osteoarticular disorders (fractures, dislocations, bone neoplasms, degenerative lesions, congenital anomalies, osteomyelitis and septic arthritis) are uncommon or rare in the ferret, and they are easily detectable radiographically.
In all cases of trauma, two full-body X-ray views (lateral and ventrodorsal) should be performed, in order to detect possible bone lesions. In the presence of a clinically evident lesion to a limb it can be useful to take X-rays of the controlateral limb for comparison and to have the normal anatomy as reference. The evaluation of bone lesions always requires two orthogonal views.