Diagnostic Approach in Canine Intervertebral Disc Disease: Integrating Radiography, CT, MRI, and CSF Analysis

Diagnosis of intervertebral disc disease (IVDD) has evolved significantly, with advanced imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI) now forming the cornerstone of accurate diagnosis. These modalities have clearly demonstrated superiority over conventional techniques like plain radiography and myelography in evaluating disc extrusion and spinal cord compression¹. 

Radiography: Initial but Limited Assessment 

Plain radiography remains widely used in veterinary practice due to accessibility; however, its diagnostic limitations are well recognized in IVDD cases. Radiographic findings suggestive of disc extrusion include narrowing of intervertebral disc (IVD) space, facet joint narrowing, intervertebral foramen opacity, presence of mineralized disc material within the vertebral canal, and vacuum phenomena. 

Although diagnostic accuracy for identifying affected disc spaces ranges between 51% and 94.7%, radiographs fail to provide critical information regarding the extent of disc extrusion, lateralization, and degree of spinal cord compression. Therefore, their role is primarily supportive, useful for ruling out other spinal pathologies rather than confirming IVDD². 

Myelography and CSF Evaluation 

Myelography, once a key diagnostic tool, has now largely been replaced by advanced imaging. When used, it may be combined with CT for improved accuracy. Diagnostic features include thinning, deviation, or discontinuity of contrast columns, asymmetric contrast distribution, and diffuse narrowing beyond the affected disc space. Reported sensitivity ranges from 53% to 97%¹. 

However, limitations include reduced accuracy in lateralization assessment and poor visualization in cases of severe spinal cord inflammation, which can complicate surgical planning. Additionally, it carries procedural risks such as transient neurological deterioration and post-myelographic seizures, particularly in large breed dogs or those receiving high contrast volumes. 

Cerebrospinal fluid (CSF) analysis is often performed prior to myelography. Pleocytosis is detected in approximately 51% of dogs with IVDD, being more common in thoracolumbar (61%) than cervical (23%) lesions. Increased macrophage presence is associated with poor recovery of ambulation in dogs lacking deep pain perception. Protein elevation is more frequent in cervical extrusions (60%) compared to thoracolumbar cases (16%), while delayed cases (>7 days) often show lymphocytic predominance, suggesting chronic inflammatory changes¹. 

Computed Tomography (CT): Rapid and Practical Imaging Tool 

CT is widely used due to its speed, accessibility, and lower cost compared to MRI. It demonstrates high sensitivity (81–100%), particularly in chondrodystrophic dogs with mineralized disc material¹. 

Characteristic CT findings include hyperattenuating disc material within the vertebral canal, loss of epidural fat, and spinal cord distortion. Importantly, CT allows differentiation between acute and chronic disc material based on morphology: acute extrusions appear well-defined and homogeneous, whereas chronic lesions are fragmented or mixed with fibrous tissue¹. 

Despite its advantages, CT has limitations. Its diagnostic accuracy decreases in older dogs (>5 years) due to incidental disc mineralization and in small dogs (<7 kg) due to reduced spatial resolution. Additionally, CT cannot adequately evaluate intramedullary spinal cord lesions, limiting prognostic interpretation^1,2,3. 

Magnetic Resonance Imaging (MRI): Gold Standard 

MRI is currently the gold standard for IVDD diagnosis, with sensitivity exceeding 98.5%. It provides superior visualization of spinal cord compression and intramedullary pathology^1,3. 

Typical findings include extradural compression, loss of T2 hyperintensity of nucleus pulposus, and hypointense extradural masses on both T1- and T2-weighted sequences. Spinal cord compression is classified as mild (<25%), moderate (25–50%), or severe (>50%) based on reduction in cord diameter¹. 

Certain MRI features are associated with poor prognosis, including extensive intramedullary T2 hyperintensity, T2 hypointensity, and CSF signal attenuation on HASTE/T2* sequences, all of which may indicate increased risk of adverse neurological outcome and Progressive Myelomalacia (PMM)¹. 

Conclusion 

While CT is often preferred for rapid assessment in acute chondrodystrophic cases, MRI remains essential for comprehensive evaluation, particularly in complex or prognostically uncertain cases. Diagnostic modality selection should be guided by clinical presentation, available resources, and required diagnostic precision.  

Reference 

1. Gómez Álvarez I, Verdes García JM, Espino López L. Intervertebral disc disease in dogs. InPets 2025 Jun 20 (Vol. 2, No. 3, p. 26). MDPI. https://www.mdpi.com/2813-9372/2/3/26 

2. Da Costa RC, De Decker S, Lewis MJ, Volk H, Moore SA, Olby NJ, Levine JM, Jeffery ND, Mullins ME, Nout-Lomas YS, Fenn J. Diagnostic imaging in intervertebral disc disease. Frontiers in veterinary science. 2020 Oct 22;7:588338. https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2020.588338/full?utm_source=chatgpt.com 

3. Emery L, Hecht S, Sun X. Investigation of parameters predicting the need for diagnostic imaging beyond computed tomography in the evaluation of dogs with thoracolumbar myelopathy: retrospective evaluation of 555 dogs. Veterinary Radiology & Ultrasound. 2018 Mar;59(2):147-54. https://doi.org/10.1111/vru.12576