Thoracic and Abdominal Radiography

Each clinic should obtain normal thoracic and abdominal films with their equipment in a 1 and 3 day-old foal for reference.

I. Thoracic Radiography [1]

It has been difficult to adequately assess the neonatal foal's respiratory system with the standard techniques of auscultation and percussion. Ultrasound is a useful tool. Radiography can significantly aid in the detection of respiratory conditions, determination of therapy and in monitoring the response to therapy. Radiographic findings should be interpreted in a serial fashion whenever possible. Patterns seen tend to be overlapping amongst specific neonatal disorders.

1. Normal - Right lateral recumbency position.

1. Exposure should allow penetration to clearly outline thoracic dorsal spinous process [2].
2. Examine rib borders and trabecular bone patterns for evidence of motion blurring [2].
3. Clear lung fields within 12 hours of birth [2].
4. Heart and pulmonary vasculation are well defined without notable interstitial or bronchial pattern [2].

2. Radiographic Patterns

1. Sites affected

1. Caudal-ventral and cranial-ventral region abnormally can indicate pneumonia or edema.
2. Both caudal-ventral and caudo-dorsal may indicate pneumonia, edema or atelectasis.
3. Diffuse lung changes can be associated with septicemia (blood borne pneumonia), edema, atelectasis, viral pneumonia.

2. Immature and septicemic foals.

1. Diffuse marked interstitial pattern.

3. Respiratory distress syndrome.

1. Granular pattern progresses to complete pulmonary opacification with air bronchograms.
2. Represents atelectasis and congestion.

3. Other thoracic radiograph findings

1. Fractured ribs, diaphragmatic hernia, pleural effusion, size of heart, vertebral fractures or osteomyelitis.

4. Techniques

1. Portable analog, and portable digital DR and CR systems
   up to 120 kVp (20-40 mA)
2. Stationary hospital units
   up to150 kVp (500 mA)
3. Analog films / Digital Sensors
   Size up to 17 inches
   Resolution for digital: up to 3 megapixels
4. Standing lateral view or right lateral recumbency - two views possible

1. Cranial lung field
2. Caudal lung field

5. Ventrodorsal views may be possible in young neonate
6. Film focal distance - 100 cm.

1. In foals <1 week old we have used 90 kVp, 10 MA with a time of 0.10-0.2 seconds (higher figure for cranial view).
2. Larger machines 80 kVp and 5 MA [2].

Each practice will have to develop their own technique chart based on their machines. Foals with higher respiratory rates are more difficult to obtain adequate quality films because of motion artifacts.

II. Abdominal Radiographs [1]

Standing lateral radiographs of the neonatal foal's abdomen provides added information when colic symptoms or abdominal distension is present. In general, foals have increased amounts of gas in the small and large intestine. Use radiographs in conjunction with clinical findings to make a diagnosis.

1. Normals (Plain standing left lateral films) [3]

1. Gas cap over fluid and ingesta in stomach.
2. Small collections of gas in the small intestine in the cranial and mid-central abdomen.

1. Cannot easily identify individual loops to determine size in foals.

3. Gas caps over fluid and ingesta in the cecum and large colon in the cauda dorsal abdomen.

1. Cannot localize within a specific large intestine structure.

4. Small amounts of gas in the small colon and ± gas in the rectum.

2. Obstructions - In general are characterized by markedly increased gas distension within the affected segments. Mechanical or functional ileus cannot be radiographically distinguished by plain films.

1. Gastric Distension may be associated with:

1. Gastric ulcers
2. Pyloric stenosis
3. When in combination with small intestine distension indicates small intestine obstruction.

2. Small Intestine

1. Distension of small intestine seen as multiple, tubular, gas filled loops with folding turns and vertical orientation in cranio-dorsal abdomen.
2. Comparing width of a distended small bowel to the length of the lumbar vertebrae has been used to evaluate distension.
          i. A ≥ 1:1 ratio of small intestine width: lumbar vertebrae length has indicated distension.
3. Distension causes are adhesions, volvulus, ileus, impactions, incarceration within mesodiverticular band, diaphragmatic hernia, large colon impaction, aganglionosis.

3. Large Intestine

1. Distension seen as large volumes of gas within markedly widened loops.
          i. With complete obstruction can fill entire abdomen with distended bowel.
          ii. Complete or long standing may produce secondary small intestine distension.
2. Many foals with large intestine distension have impactions which may often be managed medically.
3. Presence or absence of gas in the rectum not correlated with any abnormalities.

4. Gastrointestinal Rupture

1. Free peritoneal gas may be noted by increased visualization of kidney and serosa of intestine.

3. Enteritis

1. Foals often present with abdominal pain.
2. Characterized by an increased volume of gas accumulation throughout GI tract without discrete distended loops of intestine.
3. Laboratory work often shows a degenerative left shift and peritoneal tap is often normal in enteritis.
4. Difficult to distinguish enteritis and obstruction.
5. Diagnosis is based on a combination of clinical signs, hematology, radiography, and response to therapy.

4. Gastrointestinal Contrast Study [4]

1. In foals less than 14 days of age, fasted for 4 hours, a dose of 5 ml/kg of a 30% weight/volume barium suspension produces:

1. Gastric emptying within 2 hours [4].
2. Barium transit time to transverse colon of approximately 3 hours.

2. Barium enemas have aided the diagnosis of colonic atresia.
3. Obstructive disorders due to strangulations or incarceration of a portion of bowel may be identified.
4. Retrograde contrast radiography [5] (180 ml/foal up to 20 ml/kg of a 30% weight/volume barium sulfate suspension) has a 100% sensitivity and specificity for evaluating obstructions in the transverse and small colon. It is slightly less sensitive (86%) and specific (83%) to evaluate the entire large colon [5]. Small NGT or Harris flush enema tube (Seamless Hospital Products Co., Wallingford, CT) can be passed into rectum. Do not force or pump barium into the tube, allow passage by gravity flow (avoid rectal tear).
5. Contrast cystography for the detection of ruptured bladder. Use an aqueous based, organic, iodine solution via urethral catheterization.

5. Necrotizing enterocolitis [6]

1. Seen in foals less than 48 hours of age.
2. Intraluminal gaseous distension.
3. Pneumatosis intestinalis or intramural air.

1. Produces a bubbly pattern
2. Intramural air is seen as:
          i. Localized cystic collections
          ii. Diffuse linear strips
          iii. Ring-shaped areas of radiolucency
3. Bowel perforation may appear as free gas in the abdominal cavity.

6. Techniques

1. Standing lateral films

1. 26 inch FFD
2. 90 or 100 KVP
3. 10 MA
4. 0.25-0.3 seconds
5. Rare earth screens
6. High speed film