The Five Types of Disc Herniation (that we know of!)
'Tis CE season so I thought it would be fun to pull up this old TidBit Tuesday from 2020 and refresh our memories about the different types of disc herniation that may be diagnosed in dogs. I hope you enjoy this light reading on your midsummers morning!
Dystrophic calcification secondary to chondroid degeneration of nucleus pulposus (NP), is called Hanson Type I. This causes mechanical stress on the outer annulus fibrosus (AF), leading to rupture of individual collagenous strands of AF and eventually full failure and extrusion.
Fibrous degeneration occurs when fibers of the disc split leading to accumulation of tissue fluid and plasma between the annular fibers. Over time the mechanical pressure exerted by NP causes thickening of the AF dorsally, causing protrusion. (Hanson Type II).
ANNPE (Acute noncompressive nucleus pulposus extrusion) - this is normal (probably) NP that is exploded into the canal, usually during high activity. Also called a traumatic disc herniation by some folks.
AHNPE (Acute hydrated nucleus pulposus extrusion) – An apparently normally hydrated NP that is compressive and often located ventral to the cord in the cervical spine.
There may be significantly more neuro deficits and less signs of cervical pain with AHNPE compared to other causes of cervical myelopathy.
FCE (Fibrocartilaginous embolism): a piece of material histologically similar NP that becomes dislodged and finds its way into the vasculature surrounding the spinal cord. This can be into venous or arterial blood vessels. The end result is an acute shift in blood flow at the level of the spinal cord.
Match the clinical sign with the type of disc herniation
A. Chronic, progressive ataxia progressing to paresis
B. Acute, non-progressive unilateral weakness affecting one leg, or one side (hemiparesis)
C. Acute, progressive, painful ataxia progressing to paresis in a chondrodystrophic dog
D. Acute non-progressive ataxia and paresis affecting both sides of the body (paraparesis or tetraparesis)
E. Acute, rapidly progressive tetraparesis and ataxia of all four limbs with minimal cervical pain
If you answered...
Type I: C
Type II: A
ANNPE: D
AHNPE: E
FCE: B
you are correct!
Based on the clinical picture, it can be very difficult to distinguish Type I from ANNPE, and AHNPE. Typically, type I is painful (but not always), and the other two are minimally to non-painful.
Which of these require surgery?
Any disc herniation that results in compression of the spinal cord with associated clinical signs could be considered for surgical correction. This statement would then suggest that Type I, Type II and AHNPE could be surgically corrected. Therefore, any patient with signs of a progressive or painful myelopathy should be evaluated for diagnostic imaging (typically MRI) for possible surgical intervention whenever possible.
Thanks for reading! I hope you have a wonderful week. As always, reach out if I can help you, help your patients, with neurologic disease.