Differential Diagnosis in Neurology

6.5. Lumbosacral Root Disease L1–L5; S1–S5

• General features:
  • Higher lumbar root involvement:
    • Autoimmune processes
    • Connective tissue diseases
    • Retroperitoneal processes (tumors, hemorrhage, fibrosis)
    • Diabetes
    • Vasculitic processes
  • Lower root involvement L4–S1:
    • Degenerative disc disease
    • Lumbar spondylolysis
    • Lumbar spondylolisthesis
    • Spinal stenosis
    • Facet hypertrophy
    • L5, S1 recess syndrome
    • Surgical procedures
  • Combined lumbosacral root disease:
    • Tumors (metastatic)
    • Surgical and post-surgical complications
    • Arachnoiditis
    • Congenital abnormalities

Congenital Defects of Lumbosacral Roots

• Scoliosis and lordosis:
  • Neurapraxia of nerve roots of contralateral side (side opposite scoliosis)
  • More susceptible to further compression by disc or bone or ligament involvement
  • Sharp angle of L5 on S1; the more towards 180° plane > pressure on L4–L5–S1 roots
• Conjoined nerve roots:
  • May occur at any level; two spinal nerves exit one neural foramina
  • Radicular symptoms at segmental level
  • Symptomatic frequently after trauma
• Lumbosacral perineural cysts:
  • Cystic dilatations of the lumbosacral nerve roots at or distal to the junction of the posterior root or DRG
  • Wall is composed of perineurium and neural tissue
  • Most often asymptomatic
  • Most often sacral nerve roots are involved if there is sciatic pain
  • Occasional hypertrophy of leg muscles innervated by specific roots
• Cyst of the ligamentum flavum:
  • Usually sacral
  • Sciatic nerve pain
• Achondroplasia:
  • Block vertebrae
  • Short pedicles
  • Narrowed exit foramina
  • Spinal stenosis with nerve root entrapment at T11–T12
• Congenital spinal stenosis:
  • Trefoil appearance of the spinal canal particularly at L4–L5
  • Narrow diameter of the canal
  • Short thickened pedicles with compromised nerve exit foramina
• Congenital narrowing of lateral recess of L5 and S1 (nerve foraminal exit canals)
  • Exit foramina congenitally compromised
  • S1 > L5 level
  • Chronic radicular symptoms; usually become symptomatic after repetitive motion injury or trauma
  • Associated with abnormalities of the sacrum
  • Urinary symptoms may occur concomitantly
• Tethered cord:
  • General Features:
    • Traction of the conus medullaris and cauda equina by tight, thickened filum terminale
    • Two clinical groups:
      • Asymptomatic in childhood and present for the first time in adult life
      • Patients with pre-existing static skeletal/neurologic abnormalities that progress in adult life
  • Clinical features:
    • Pes cavus
    • Cutaneous stigmata (strawberry hemangioma; cutaneous dimple) over the sacrum
    • Back pain; may have anal and perianal pain; gluteal or diffuse leg pain
    • Motor and sensory radicular deficit (L5–S1) is rare
    • Sphincter function depressed
    • Associated with terminal syringomyelia (caudal 1/3 of the cord)
    • Associated with diastematomyelia
    • Associated with lipoma of the conus and lipomyeloschisis
    • May be associated with pes cavus of one foot
    • Urgency symptoms of spastic neurogenic bladder
    • Symptomatic with specific positions; particularly the dorsal lithotomy position
    • Symptomatic following delivery or vaginal surgery (dorsal lithotomy position)
  • Urodynamic findings:
    • Hyperreflexia of the bladder
    • Internal and external detrusor-sphincter dyssynergia
    • Decreased sensation (bladder)
    • Decreased compliance (bladder)
    • Hypo contractility of detrusor muscle
  • MRI:
    • Tethered cord; tip of the conus medullaris below the body of L2 instead of the L1–2 disc space
    • Associated with intra or extradural lipoma

Classification of Lumbosacral Nerve Root Anomalies with Tethered Cord

• Type I and II
  • One or more nerve roots exit the thecal sac at a more cranial (Type I) or caudal (Type II) level
• Type III
  • Two or more roots emerge from the thecal sac through a closely adjacent dural opening
• Type IV
  • Two or more roots emerge from the dural sac as one nerve trunk
• Type V
  • Two or more roots are connected by an anastomotic branch after exiting the dural sac

Clinical Characteristics of Congenital Root Anomalies

• Anomalies primarily of L5 and S1:
  • Type III and IV most common anomaly
  • 20% of patients have other lumbosacral anomalies; rarely congenital absence of a facet joint on the side of the anomaly
  • Clinical symptoms are severe
  • Reduced mobility of the anomalous roots
• Extra foraminal stenosis of the lumbosacral spine:
  • Affected roots are compressed between the transverse process of the last lumbar segment and sacral ala
• Conjoined lumbosacral roots:
  • Found in 1% of lumbar disc operations
  • L5–S1 level
  • Often not associated with a herniated disc
  • Radiographic features:
    • Asymmetric subarachnoid space
    • Widened axillary pouch
    • Two or more individual nerve roots in the axillary pouch

Degenerative Diseases Affecting Lumbosacral Nerve Roots

• Degenerative Disease of Lumbar and Sacral Roots
  • Disc disease: L4–L5; L5–S1 primarily
    • Free fragment (penetrates posterior longitudinal ligament)
    • Schmorl's nodes (vertebral midline herniation)
    • Far lateral disc (L1–S1)
  • Lateral recess syndrome (L5; S1)
  • Spinal stenosis (spondylosis, ligament, facet hypertrophy)
  • Facet hypertrophy (trophism)
  • Synovial cyst of the facet joint
  • Osteophyte formation in the foraminal exit canal
  • Spondylolisthesis

• Differential Diagnosis:
  • Disc disease
  • Spondylosis
  • Degenerative spondylolisthesis
  • Foraminal exit arthritis (osteophytes)
  • Facet hypertrophy (tropism and rotation)
  • Stenosis (disc; spondylosis, ligamentous hypertrophy)
  • Synovial cysts of facet joints

Benign Bone Tumors Affecting Lumbosacral Nerve Roots

Benign Osteoblastic Tumors

• Osteoid osteoma/osteoblastoma
  • Lamina and pedicle often involved
  • Pain is often nocturnal and relieved by aspirin > narcotics (prostaglandin dependent)
  • Radicular pain in 50% of patients
  • Tenderness in the area of the lesion
  • Osteoblastomas frequently extend into the neural exit foramina
  • Painful scoliosis is a common presentation

Osteochondroma

• Osteochondroma comprises approximately 50% of benign bone neoplasms
• Involvement of the spine in 2.5–5% of cases; spine involvement often seen in a setting of multiple osteochondromatosis
• Usual occurrence is in long bones
• Usual spine predilection is for cervical or upper thoracic levels
• Cases described at L4 and L5 with radicular involvement

Extraosseous Extension of Vertebral Hemangioma

• Asymptomatic vertebral hemangiomas are common
• Extraosseous extension can cause intracanalicular and spinal cord compression

Aneurysmal Bone Cyst

• Benign, sometimes expansive and destructive (osteolytic)
• Occurs most frequently between 10–20 years of age
• Posterior elements of the spine involved with extension into the vertebral body
• Annual incidence 0.14/100,000 people; age range 1–59; slightly more common in females than males
• Most commonly found in the metaphyseal areas of long bones

Dermoid

• Dermoid cysts are intradural in the lumbar and sacral spine
• Rupture causes chemical arachnoiditis
• May occur at site of meningocele repair
• Midline dermal sinus (may be associated)
• Paravertebral dermal sinus
• May be associated with meningitis
• Associated with spina bifida

Lipoma

• Association:
  • Tethered cord
  • Anorectal malformations
  • Meningocele
  • Sacral agenesis (caudal regression syndrome)
  • Lumbar vertebral dysgenesis
  • Lumbosacral skin lesions: tufts of hair, skin tags, pigmental nevi, hemangiomas

Rare Benign Bone Lesions that Can Affect Axial Skeleton with Consequent Radiculopathy

• Giant cell tumor of bone
• Leiomyomas
• Chondromyxoid fibroma
• Fibrous histiocytoma
• Differential points for malignancy or benignancy
  • Pedicle change with expansion is most often malignant
  • Normal marrow preservation of a collapsed vertebral body on T1, on an MRI sequence is most compatible with an osteoporotic fracture