10-year anniversary-is this an intestinal mechanical obstruction?

RADIOGRAPHIC DIAGNOSIS OF MECHANICAL OBSTRUCTION IN DOGS BASED ON RELATIVE SMALL INTESTINAL EXTERNAL DIAMETERS

Cyrielle Finck, Marc-André D'Anjou, Kate Alexander, Swan Specchi, Guy Beauchamp

Background
Mechanical intestinal obstruction is a frequent cause of acute vomiting in dogs and requires timely diagnosis to improve outcomes. Radiography is commonly used for its availability and cost-effectiveness compared to ultrasonography. This study aimed to evaluate the diagnostic value of radiographic measurements, particularly the small intestinal diameter ratios, and patterns of dilation for diagnosing mechanical obstruction in dogs.

Methods
A retrospective study included 50 dogs divided into two groups: 25 with confirmed mechanical obstruction (via surgery or necropsy) and 25 without obstruction (based on follow-up or alternative diagnosis). Radiographs were analyzed by three examiners for:
-Intestinal dilation patterns (segmental, regional, or diffuse) and severity.
-Measurements of maximum (SImax), minimum (SImin), and average (SIave) small intestinal diameters and the L5 vertebral height.
-Calculated ratios: SImax/L5, SImax/SImin, and SImax/SIave.
-Thresholds for diagnosing obstruction were determined using receiver operating characteristic (ROC) analysis.

Results
Dilation Patterns: Segmental dilation was significantly more common in obstructed dogs (44–56%), while absence of dilation was more prevalent in non-obstructed dogs (20–76%). Interobserver agreement was poor to fair for identifying dilation patterns (κ = 0.16–0.57).

Ratios: All three ratios (SImax/L5, SImax/SImin, SImax/SIave) were significantly higher in obstructed dogs:
-SImax/L5: Threshold values of 1.4–1.6 (rule out obstruction) and 2.4–2.8 (high probability of obstruction).
-SImax/SImin: Thresholds of 2.0–2.1 (rule out) and 3.4–6.2 (high probability).
-SImax/SIave: Thresholds of 1.3–1.4 (rule out) and 1.9–2.6 (high probability).

Interobserver Variability: Measurement reproducibility was moderate for SImax/L5 (coefficient = 0.61) and lower for SImax/SImin and SImax/SIave (0.35–0.44).

Limitations
Some radiographs had visible foreign bodies, potentially biasing the results.
Cases with poor abdominal serosal detail were excluded, limiting generalizability.
Reader variability and reliance on subjective interpretation affected the consistency of findings.

Conclusions
Radiographic evaluation using small intestinal ratios and dilation patterns can aid in diagnosing mechanical obstruction. The study provides thresholds to guide clinical decision-making:

-Dogs with ratios below the lower thresholds are unlikely to have obstruction and may not require further testing.
-Ratios above the higher thresholds strongly suggest obstruction, supporting surgical intervention if other diagnostics are unavailable.
-Ratios within the gray zone warrant additional diagnostic tests like ultrasonography.
-Radiographic findings should be used alongside clinical signs to optimize decision-making in suspected obstruction cases.

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