Ultrasound vs X-ray: What Each Reveals in Foreign Body Obstructions

Foreign body suspicion is one of those all-too-familiar moments in general practice – the vomiting dog that “got into something,” the cat with sudden pain and abdominal tension, or the young Labrador that looks far too pleased with itself. The challenge isn’t just confirming the obstruction; it’s knowing which imaging tool will provide the fastest, safest, and most actionable answer. Radiographs and ultrasound each offer advantages, but they reveal different things, and that’s where diagnostic strategy matters.

Many GPs face the familiar question: “Should I start with X-rays, ultrasound, or both?” The answer comes down to what you’re looking for. Metal, bone, and other dense objects appear quickly on radiographs, providing instant clarity. But wooden skewers, plant material, fabric, string, rubber and plastic often disappear on X-ray, leaving you with a normal film despite a dog that’s clearly uncomfortable.

That’s where ultrasound shifts the picture. It can visualise non-radiopaque material, assess bowel wall thickness, pinpoint focal pain, detect free fluid and show reduced or absent motility in obstructed segments. In many cases, we see across Adelaide and regional SA, particularly with wooden skewers, corn cobs, fabric, and plant material, ultrasound is the modality that answers the “is something in there?” question long before radiographs can.

Ultrasound is often the missing piece in foreign body diagnosis, particularly when radiographs appear normal, but your clinical instincts suggest otherwise. SA Vet Sonography provides on-site, real-time assessment, giving you fast clarity without sending the patient off-site or delaying treatment. Being able to visualise non-radiopaque objects, assess bowel wall integrity, detect free fluid, and evaluate motility helps determine whether surgery is urgent, whether stabilisation should be prioritised, and how to communicate the plan clearly to owners. It’s a practical way to maintain control of the case while providing your clients with accurate and confident guidance.

Radiographs remain the fastest way to identify dense foreign material. Metallic objects, bone fragments, stones and other radiopaque items are typically obvious, saving time and providing the client a clear visual explanation. They’re also excellent for diagnosing linear foreign bodies through classic radiographic patterns – plication, gas bubbles, sentinel loops and obvious obstruction silhouettes. When you need to see gas patterns or check for free gas, nothing replaces standard films.

Ultrasound, however, offers information that radiographs simply can’t. It detects non-radiopaque objects, such as wood, plastic, and fabric. It shows bowel wall layering, thickness and vascularity, highlights focal pain, identifies free abdominal fluid, and provides real-time motility assessment. Wooden skewers, corn cobs, peach pits, rubber toys and bits of clothing are classic ultrasound wins – especially when X-rays appear deceptively normal.

In many cases, the most complete picture comes from doing both. Radiographs identify structural gas patterns and radiopaque items; ultrasound confirms material that doesn’t show up on film and assesses complication risks such as perforation or devitalisation. This combined approach helps prioritise surgery vs stabilisation, improves client communication and supports cost-conscious decision-making.

Most foreign body cases tolerate gentle handling well, but anxious or painful patients may need mild sedation to allow adequate ultrasound contact and minimise discomfort.

If you’d like help interpreting inconclusive X-rays or need a targeted ultrasound assessment for a suspected obstruction, we’re always happy to assist.