Thoracolumbar Intradural Disc Herniation in Eight Dogs: Clinical, Low‐field Magnetic Resonance Imaging, and Computed Tomographic Myelography Findings

Abstract

Intradural disc herniation is a rarely reported cause of neurologic deficits in dogs and few published studies have described comparative imaging characteristics. The purpose of this retrospective cross sectional study was to describe clinical and imaging findings in a group of dogs with confirmed thoracolumbar intradural disc herniation. Included dogs were referred to one of four clinics, had acute mono/paraparesis or paraplegia, had low field magnetic resonance imaging (MRI) and/or computed tomographic myelography, and were diagnosed with thoracolumbar intradural disc herniation during surgery. Eight dogs met inclusion criteria. The prevalence of thoracolumbar intradural disc herniation amongst the total population of dogs that developed a thoracolumbar intervertebral disc herniation and that were treated with a surgical procedure was 0.5%. Five dogs were examined using low-field MRI. Lesions that were suspected to be intervertebral disc herniations were observed; however, there were no specific findings indicating that the nucleus pulposus had penetrated into the subarachnoid space or into the spinal cord parenchyma. Thus, the dogs were misdiagnosed as having a conventional intervertebral disc herniation. An intradural extramedullary disc herniation (three cases) or intramedullary disc herniation (two cases) was confirmed during surgery. By using computed tomographic myelography (CTM) for the remaining three dogs, an intradural extramedullary mass surrounded by an accumulation of contrast medium was observed and confirmed during surgery. Findings from this small sample of eight dogs indicated that CTM may be more sensitive for diagnosing canine thoracolumbar intradural disc herniation than low-field MRI.

A Review of Fibrocartilaginous Embolic Myelopathy and Different Types of Peracute Non-Compressive Intervertebral Disk Extrusions in Dogs and Cats

“…Various descriptive terms have been used to indicate peracute extrusion of hydrated or degenerated intervertebral disk material generally during trauma or exercise, resulting in penetration of the dura mater and frequently also of the spinal cord parenchyma ( 23 – 37 ). In this review article, the extrusion of either hydrated or degenerated intervertebral disk material in an intradural-extramedullary or in an intramedullary location will both be referred to as IIVDE.…”

“…In this review article, the extrusion of either hydrated or degenerated intervertebral disk material in an intradural-extramedullary or in an intramedullary location will both be referred to as IIVDE. IIVDE is considered a rare type of intervertebral disk herniation and the largest published study in the veterinary literature includes eight dogs only ( 37 ). In this recent study, the prevalence of thoracolumbar IIVDE among the total population of dogs that developed a thoracolumbar intervertebral disk herniation and that underwent spinal surgery was 0.5% ( 37 ).…”

“…Intradural/intramedullary intervertebral disk extrusion has been reported in various canine breeds and in two adult cats ( 23 – 37 ). By combining data of case reports and series 26 dogs with IIVDE have been identified.…”

“…Fibrocartilaginous embolic myelopathy (FCEM) and peracute intervertebral disk extrusions (IVDEs) that are not resulting in extradural spinal cord compression have been increasingly recognized since the use of magnetic resonance imaging (MRI) has become widespread in veterinary neurology. Studies and case reports have been published on the clinical and diagnostic features of these conditions and a few studies have also investigated outcome and prognostic factors ( 1 – 37 ). However, no previous comparative review has discussed similarities and differences in clinical presentations, imaging and pathological findings, outcomes, and prognostic factors of these conditions.…”

“…Definitive diagnosis can be reached post-mortem. Definitive diagnosis has also been reached following surgery in some dogs with intradural/intramedullary intervertebral disk extrusions (IIVDEs) ( 23 , 24 , 26 – 28 , 30 , 31 , 33 – 37 ). Ante mortem diagnosis is largely supported by MRI.…”