A Summary of a lecture by Dr. Lorrie Gaschen at Zoomies 2026

Introduction

This lecture provides a wonderful comprehensive framework for interpreting gastrointestinal imaging in rabbits and other small mammals presenting with anorexia or hyporexia. The gastrointestinal tract of rabbits, as hindgut fermenters, presents unique anatomical challenges that differ significantly from dogs and cats. 

The lecture systematically explores normal radiographic anatomy, establishes objective measurement criteria, and distinguishes between functional ileus and mechanical obstruction through a case-based approach – with the emphasis on developing a systematic review process that can be applied in general practice to improve diagnostic confidence and guide clinical decision-making.

1. Systematic Radiographic Assessment Is Essential

The key to interpreting rabbit abdominal radiographs lies in a consistent, systematic approach:

• Begin with the stomach – assess its size, position, and content characteristics. The stomach should normally contain heterogeneous fibrous material and should not extend beyond the costal arch or past the caudal endplate of L2, and should not generally contact the ventral abdominal wall.
• Evaluate the cecum – the largest gastrointestinal structure in rabbits, is normally filled with fibrous content and spanning much of the ventral abdomen. Cecal size and content provide valuable information about gastrointestinal motility.
• Check for faecal pellets in the distal colon – a chain of individual pellets confirms ongoing movement through the gastrointestinal tract. Absence of pellets suggests stasis or obstruction.
• Assess the small intestines – normally difficult to identify and should measure less than 1.5 times the height of the L5 vertebral body. They typically occupy the area between the cecum and distal colon, often more prominent on the left side.
• The sacculus rotundus appears as a small “bagel” or “donut” structure in the mid-right abdomen at the origin of the first cecal gyrus – knowing its normal location helps identify pathology such as abscesses or diverticula.

2. Objective Measurement Criteria for Gastric Size

Vertebral Stomach Score (VSS) – measured similarly to the vertebral heart score, using the long and short axes of the stomach at 90-degree angles, counted against vertebral lengths starting at L1:

• Normal range for rabbits without gastrointestinal disease: 5.2–9.2
• Range in rabbits with confirmed disease: 5.7–12.5
• A score above 9.2 warrants concern and further investigation

Additional objective measurements include:

• Sum of gastric height and width compared to the L1-to-hip length – when the stomach measurement exceeds this length, it suggests enlargement
• Caudal margin of the stomach should not extend past the cranial endplate of L2
• The ventral stomach margin contacting the abdominal wall indicates significant distension
• These measurements are valuable tools for increasing confidence, particularly for less experienced interpreters, but must be considered as one piece of the overall clinical picture

3. Distinguishing Functional Ileus from Mechanical Obstruction

Differentiating between stasis and obstruction is critical for management decisions:

Functional ileus (gastric stasis) typically presents with:

• Stomach containing heterogeneous fibrous content with minimal surrounding gas
• Stomach may be mildly to moderately distended but remains within normal positional limits
• Cecum may be normally filled, reduced in size, or fluid-filled (dysbiosis)
• Faecal pellets may be reduced or absent in the distal colon
• Small intestines show generalised mild gas dilation without severe segmental distension
• Often secondary to pain from dental disease, osteoarthritis, or other underlying conditions

Mechanical obstruction demonstrates a more dramatic pattern:

• Stomach filled with fluid and gas rather than normal fibrous material – the “fluid and gas cap” sign
• Stomach distension beyond L2 with ventral wall contact
• Dilated duodenum visible – an unusual finding in normal rabbits
• Small intestines may show segmental fluid or gas distension
• Cecum and distal colon appear empty or reduced to “threads”
• Obstructing material (often hairballs) may be identified on ultrasound or CT, typically in the proximal jejunum or distal duodenum

4. Normal Anatomy and Positioning for Imaging

Understanding normal gastrointestinal anatomy is fundamental to identifying abnormalities:

• The fundus is normally located on the left side, with the antrum positioned on the right – the antrum has a characteristically thick muscular wall that serves as a useful landmark
• The first and second cecal gyri arise from the sacculus rotundus and curve to become the third cecal gyrus, which terminates at the cranioventral abdomen, immediately caudal to the gastric antrum
• The appendix originates at the termination of the third cecal gyrus and courses obliquely from right cranioventral to left mid-caudal abdomen – normally difficult to visualise but becomes apparent when diseased
• The proximal colon follows a similar oblique trajectory but can be identified by its characteristic haustra on ultrasound or CT
• Small intestinal segments occupy the region wedged between the cecum ventrally and distal colon dorsally

Positioning recommendations:

• Rabbits should be stretched out, not hunched – using padding and sedation to achieve proper extension
• Unlike dogs, a three-view series (right lateral, left lateral, VD) is not always necessary, though it can be helpful for assessing fluid and gas redistribution
• Whole-body imaging is typical for small mammals, capturing chest and abdomen together
• A two-view study (one lateral and VD) is often sufficient for routine assessment

5. CT and Ultrasound as Advanced Diagnostic Tools

Computed tomography has become the gold standard for gastrointestinal imaging in small mammals:

• CT provides superior evaluation of liver lobe torsion, which appears as a hypoattenuating, non-enhancing lobe due to ischaemia – a common cause of hyporexia in rabbits
• Contrast administration (600 mg iodine/kg) is essential, with scanning starting 30–45 seconds after injection
• Delayed scans (60–120 seconds) are recommended to ensure contrast reaches the urinary tract
• Thin-slice acquisition (0.6 mm) with overlapping intervals prevents “stair stepping” artefacts and enables multiplanar reconstruction

Ultrasound remains a valuable complementary tool:

• Useful for tracing the duodenum from the stomach to identify obstructive material
• Can identify appendicitis and sacculitis, which are often impossible to diagnose radiographically
• Ultrasound shows wall thickening, fluid content, and granular material in inflamed structures
• The proximal colon’s haustra are well-visualised on ultrasound, helping distinguish it from the appendix

Specific CT findings:

• Obstructing hairballs appear as hyperattenuating soft tissue structures (60+ Hounsfield units) within fluid-dilated intestinal segments
• GDV is definitively diagnosed on CT by identifying the antrum on the wrong side (left instead of right)
• Appendicitis shows a distended, fluid or gas-filled appendix with possible necrotic content
• Sacculitis presents with wall thickening and abnormal granular or fluid content

6. Specific Diseases and Their Imaging Features

Gastric Dilatation and Volvulus (GDV):

• Occurs in rabbits and guinea pigs, similar to dogs
• In rabbits, the normal fundus position (left) is displaced to the right, with the antrum on the left
• DV radiographs are most helpful for identification, though CT is superior
• GDV can cause bile duct obstruction due to the oesophagus being more centrally located at the porta hepatis in rabbits, leading to elevated liver enzymes and possible icterus
• In guinea pigs, GDV appears as a right-sided, gas-filled stomach (instead of the normal left-sided position)

Appendicitis and Sacculitis:

• Appendicitis appears as a distended appendix with fluid, impacted gas, or mixed granular content, coursing obliquely from right cranial to left mid-caudal abdomen
• Sacculitis presents with sacculus rotundus wall thickening and abnormal content, which may develop into abscesses or diverticula over time
• Both conditions are best diagnosed with ultrasound or CT; radiographs are often unremarkable
• Necrotic appendicitis can cause severe systemic illness, including hypothermia and shock

Cecal Impaction:

• Associated with GI stasis, the cecum appears distended with large volume content
• Content may show increased, partially mineralised opacity due to drying
• Ultrasound or CT provides better characterisation than radiographs alone

Liver Lobe Torsion:

• A potential cause of GI stasis and hyporexia
• Best identified with CT where the affected lobe is hypoattenuating and non-enhancing
• Primarily affects the caudate lobe
• Associated with elevated liver enzymes on blood work

Other Considerations:

• Pancreatitis requires CT or ultrasound for diagnosis
• Dental disease and osteoarthritis must be ruled out as sources of pain in anorexic rabbits
• Orthopaedic changes are highly relevant; even minor pain can significantly impact feeding behaviour

7. The Decision-Making Process

Approach to the anorexic or hyporexic rabbit:

Step 1 – Radiographic assessment:

• Evaluate stomach size, content, and position
• Assess cecal size and content
• Check for faecal pellets in the distal colon
• Examine small intestinal segments for dilation
• Rule out GDV by confirming normal fundus position

Step 2 – Interpretation:

• Fibrous content in the stomach with normal-size cecum and fecal pellets suggests a functional problem (pain, dental disease, liver disease, kidney disease)
• Fluid and gas in the stomach with dilated small intestine and empty cecum/colon suggests mechanical obstruction – the animal requires urgent attention
• Diffuse gas dilation with small cecum and no fecal pellets suggests enteritis or dysbiosis

Step 3 – Next steps:

• For equivocal cases, consider “treat and repeat” – fluid therapy, analgesia, and repeat radiographs in 12–24 hours
• Ultrasound can trace the small intestine to identify obstructive material
• CT provides definitive diagnosis for liver lobe torsion, appendicitis, sacculitis, and pancreatitis
• Mechanical obstruction requires surgical intervention without delay

Key principles to remember:

• Pain management is crucial – these rabbits suffer from significant discomfort
• Always consider extra-gastrointestinal causes such as dental disease, osteoarthritis, liver disease, and kidney disease
• Positional radiographs (right and left lateral) help redistribute fluid and gas for better visualisation
• Objective measurements increase diagnostic confidence but must be interpreted in context

Conclusion

This lecture provides a structured, practical approach to gastrointestinal imaging in rabbits and other small mammals. By understanding normal anatomy, applying objective measurements, and systematically evaluating radiographic findings, clinicians can distinguish functional ileus from mechanical obstruction and guide appropriate management. Advanced imaging modalities such as CT and ultrasound offer superior diagnostic capabilities for specific conditions including appendicitis, sacculitis, liver lobe torsion, and GDV. Radiography remains the essential first-line tool, with the “treat and repeat” approach offering a safe and effective strategy in equivocal cases.