By Ruth Van Hatten, DVM, DACVR
Abdominal radiography is a common diagnostic test used in all veterinary hospitals ranging from academic teaching hospitals to small private practices. Along with blood work and the physical exam, it is an invaluable asset in diagnosing a variety of abdominal diseases ranging from mechanical obstruction from foreign bodies to cystic calculi causing hematuria. This article will describe a few helpful tips to assist in interpreting abdominal radiographs.
Vomiting is one of the most common presenting complaints at emergency hospitals, and abdominal radiography is commonly performed to determine if surgery is warranted. Orthogonal radiographs are always recommended with the RLAT (right lateral) and VD (ventrodorsal) views most often performed; however, I recommend obtaining three view (LLAT (left lateral), RLAT, and VD) abdominal radiographs when evaluating for a cause of vomiting. When evaluating the stomach, the fundus is located on the left side while the pylorus and duodenum are located in the right cranial abdomen. In LLAT, any gas within the stomach will rise and outline the pylorus and duodenum, where in RLAT, the gas will be located within the fundus. This is extremely helpful when evaluating for foreign material within the pylorus, pyloric masses, or linear foreign bodies that extend into the duodenum. For example, in LLAT, the gas will outline foreign material that is lodged in the pylorus that could result in a pyloric outflow tract obstruction (Figures 1 and 2).
Figure 1: Eight year old, spayed female Collie presented for three day history of vomiting, lethargy, and inappetence.
Figure 1a: Right lateral abdominal radiograph; the stomach contains a medium amount of gas and fluid. The small intestine contains a large, structured soft tissue foreign body (ie cloth) with plication (arrow).
Figure 1b: Left lateral abdominal radiograph; on this view, the arrow points to the gas-filled pylorus which better outlines the soft tissue foreign body that extends from the pylorus into the duodenum and small intestine.
Along these same lines, the RLAT is performed when evaluating for gastric dilatation and volvulus because in the abnormally positioned stomach, the gas-filled pylorus is best seen on the RLAT instead of the LLAT, and is also dorsally displaced. When evaluating the RLAT for a GDV, if it is difficult to determine if the stomach is misplaced or just distended, it is recommended to complete the study and obtain a VD radiograph. In a normally positioned stomach, the pylorus and duodenum will be located in a normal position on the right side of the cranial abdomen with the fundus on the left, where in GDV, the pylorus and cranial duodenum are displaced to the left.
Three view abdominal radiographs are also helpful when trying to evaluate for small intestinal mechanical obstruction. With the shifting of fluid and gas within the small intestine between the three different views, it is not uncommon for foreign material to be better outlined by gas on one view compared to the other views. If a radiopaque foreign body is not visible, seeing an enlarged loop of small intestine that is unchanged in location and size on multiple views (i.e. sentinel loop) is a strong suspicion for mechanical obstruction. By taking three views, it will often increase confidence in determining if the patient is obstructed vs non-obstructed.
Figure 2: Four-year-old, castrated male Labrador retriever presented for one-day history of vomiting and nausea.
Figure 2a: Right lateral abdominal radiograph; the stomach is mildly enlarged with fluid, gas, and few, small mineralized bodies. No gross small intestinal foreign body or obstruction is seen.
Figure 2b: Left lateral abdominal radiographs; the gas within the stomach rises into the pylorus and outlines a structured soft tissue foreign body (arrow) that extends into and enlarged duodenum and causes a mechanical obstruction.
When evaluating for causes of stranguria and hematuria, abdominal radiographs are performed to evaluate for the presence of radiopaque calculi within the urinary tract. One common mistake is to not include the entire urethra in the image. To better evaluate the penile urethra in male dogs, it is recommended to take two lateral radiographs. In the first radiograph, place the dog in lateral recumbency and pull the pelvic limbs caudally by extending the hips. This allows improved visibility of the urinary bladder as well as the distal aspect of the penile urethra. In the second lateral radiograph, the pelvic limbs are pulled cranially by flexing the hips. This view, on the other hand, allows visibility of the remaining penile urethra (Figure 3). It is important to remember that although most urinary calculi are radiopaque, some calculi (i.e. cysteine, urate, xanthine) are radiolucent and thus not visible on radiographs.
Figure 3: Eleven-year-old, intact male, Rhodesian ridgeback presented for stranguria and dribbling urine.
Figure 3a: A right lateral caudal abdominal radiograph; the urinary bladder is moderately distended and contains numerous small, irregularly shaped mineralized bodies. The prostate is normal in size for an intact male.
Figure 3b: A right lateral caudal abdominal radiograph with the pelvic limbs flexed; this positioning allows better evaluation of the penile urethra. The arrow points to a few, small, faintly mineralized calculi located within the urethra at the caudal aspect of the os penis.
Lastly, it is important to perform a systematic approach when evaluating radiographs each and every time and to assess each visible organ by using the Roentgen signs (size, shape, number, location, margin, and opacity). I often start with the gastrointestinal tract, as GI signs are the most often reason for the radiographs, then hepatobiliary tract, spleen, urinary tract, and genital tract. Next, I assess the abdominal serosal detail, and lastly the musculoskeletal structures. By evaluating radiographs the same way every time, there is less risk of missing both clinically and non-clinically relevant lesions.