Anatomical definition: the lumbosacral plexus is derived from spinal cord segments L4-S2. The four main peripheral nerves, arising from cranial to caudal direction are: n. femoralis, n. obturatorius, n. ischiadicus and n. pudendus. Due to the medullar ascend (disparity in lengths of spinal cord and vertebral column)are the last lumbar segments L5-7 over the 4th lumbar vertebrae and the last three sacral segments lie over the 5th lumbar vertebrae. In cats and miniature breeds of dogs is this disproportion not so significant (last three sacral segments lie over the L5-L6 vertebral bodies. The cauda equina has been defined as the spinal cord segments, the adjacent nerve roots, which include the seventh lumbar nerve root, sacral nerve roots 1-3 and caudal nerve roots 1-5, contained within the vertebrae L5-7 and S1-3 and CD1-5. Any disease affecting the region of the sixth and seventh lumbar vertebrae, sacral vertebrae or the first five caudal vertebrae can potentially lead to cauda equina lesions.
Clinical manifestation: the cauda equina is the most difficult localization in clinical neurology. The symptoms can vary from just simple pain in the L/S region, paraesthesia, difficulties in urination and defecation, automutilation of one or both hind limbs or tail, or motor and sensory deficiencies like monoparesis, paraparesis or monoplegia and paraplegia combined with incoordination of hind limbs. We can face the huge variety of all combinations or just single one of these symptoms.
Clinical neurological evaluation: depending of the precise anatomical localization: mild ataxia of hind limbs, mild monoparesis or paraparesis, decreased postural reactions (proprioceptive positioning reaction) in one or both pelvic limbs. The spinal reflexes of hind limbs are decreased (lower motor neuron)-typically flexor reflex. Extensors (patellar, tibial cranial) are often increased, because of the lack of antagonism of the flexor muscle group. Decreased tonus of the anal sphincter (rectal digital palpation including prostate palpation!) and decreased perianal reflex and bulbo- and vulvo-urethral reflexes are typical for pudendal lesions. Lumbosacral pain (by extension of pelvic limbs), recurring lameness and difficulty to stand up and going up the steps are suspicious for orthopedic problems (hip dysplasia, knee instability..).
Differential diagnoses
Dogs with localization in cauda equina (lower motor neuron lesions) the differential diagnoses list includes:
Spinal cord infarct-peracute onset, large breeds, middle aged, NON PAINFUL, lateralized, improvement after 24-36 hours
Aortic, iliac thromboembolism-acute, swollen muscles, no femoral pulse, more myopathic symptoms as neuropathic.
Discospondylitis-chronic, acute, progressive, PAIN!! No neurological deficiencies in the early stage,
Traumatic lumbosacral, sacrococcygeal fractures and luxations-peracute onset, pain, history.
Anomaly-sacrocaudal agenesis-Manx cats, Old English Sheepdogs, Boston Terriers and other tailless or short-tailed dogs, deficits present from birth, often first noted at weaning period
Neoplasia-nerve roots tumors, extradural tumors (neurofibrosarcoma, prostatic adenocarcinoma, perianal gland adenocarcinomas...) chronically progressive, painful, lateralized, older animals.
Degenerative disorders-lumbosacral spondylopathy, chronically progressive, painful, lateralized, particularly in large breed dogs.
Definitive Diagnosis
Radiography-survey radiographs are initial steps in evaluating lumbosacral disease, it is only diagnostic in conditions that involve bone destruction or displacement (discospondylitis, osseous neoplasia, fracture and subluxation). Notice, radiographic signs in discospondylitis may not be present for four to six weeks after the onset of infection. Indirect evidence of degenerative lumbosacral stenosis (e.g., spondylosis deformans, disc space narrowing, end plate sclerosis) is frequently present on survey radiographs, but do not confirm the diagnosis!!
Contrast radiography-myelography involves the injection of contrast medium (atlantooccipital), into subarachnoid space. Study with the lumbosacral junction in the neutral, flexed and extended position is recommended. If the subarachnoid space ends cranial to the lumbosacral junction, discography and epidurography should be performed. Discography consists of injection of contrast medium into the nucleus pulposus. If the disc is normal, it is not possible to inject more then 0.3ml of contrast medium. With an abnormal disc, it may be possible to inject as much as 3.0ml of contrast medium.
Computerized tomography-has better soft tissue contrast resolution and gives us cross-sectional images. Abnormalities including loss of epidural fat, increased soft tissue opacity in the intervertebral foramen, bulging of the intervertebral disc, thecal sac displacement, narrowed intervertebral foramen, thickened articular processes or their subluxation, are sings of degenerative L-S spondylopathy.
Magnetic resonance Imaging (MRI) provides soft tissue contrast that is superior to CT and there is direct visualization of the spinal cord, cerebrospinal fluid, intervertebral discs, ligaments and nerve roots. MRI can reveal loss of epidural fat, identify intervertebral disc degeneration, displaced nerve roots, foraminal protrusions or foraminal stenosis.
Electromyography of the limbs, tail and perineum may reveal denervation (spontaneous activity indicates LMN involvement). However, a normal electromyogram does not eliminate the possibility of lumbosacral disease.
Other diagnostic techniques-Blood analysis: hematology incl. sedimentation (discospondylitis), urine analysis (infections, discospondylitis, tumors), USG-aortal termination (thrombus), prostate, hemoculture and urine culture (discospondylitis)
Prognosis
Guarded to poor for aortal thrombosis (depending on duration and cause of thrombosis).
Good or guarded for discospondylitis (mostly without surgery)
Lumbosacral spondylopathy-good or guarded. Negative factors: evidence of fecal and/or urinary incontinence, megacolon, concurrent hip dysplasia or other orthopedic problems.