Spondylolisthesis is anterior (anterolisthesis) or rarely posterior (retrolisthesis) slippage of one vertebral body relative to the vertebra below. Five types are defined: Type I — degenerative (most common, L4-5, elderly women, from facet joint degeneration), Type II — isthmic/spondylolytic (most common at L5-S1, pars interarticularis defect, stress fracture in young athletes), Type III — degenerative (overlaps with Type I), Type IV — traumatic (acute fracture), Type V — pathologic (bone weakness from tumor or infection), Type VI — dysplastic (congenital facet anomaly). Meyerding classification determines degree of slippage: Grade I (<25%), Grade II (25-50%), Grade III (50-75%), Grade IV (>75%), Grade V (spondyloptosis — complete fall-off). Sagittal MRI evaluates vertebral slippage, thecal sac compression, and nerve root relationship. CT sagittal reformat best demonstrates pars interarticularis defect. Double canal appearance on axial CT (Napoleon hat sign / inverted Napoleon hat sign) is pathognomonic at the slippage level. Clinically can cause low back pain, radiculopathy, and cauda equina syndrome in severe cases.
Age Range
20-80
Peak Age
55
Gender
Equal
Prevalence
Common
In degenerative spondylolisthesis (Type I), the pathological process is: disc degeneration → disc height loss → facet joint orientation changes (sagittalization) → facet joint degeneration and instability → anterior slippage of superior vertebra over inferior vertebra. L4-5 is most common because L4-5 facets have more sagittal orientation → lower resistance to anterior slippage. In isthmic spondylolisthesis (Type II), pars interarticularis stress fracture is the main mechanism: the pars is the thinnest and weakest region of posterior elements → repetitive extension + rotation stress (athletes, gymnasts) → stress fracture → bilateral pars defect → posterior bony ring continuity is disrupted → vertebral body slips anteriorly. L5-S1 is most common because L5 pars experiences the most stress (shear forces maximum at lumbosacral junction). On MRI, thecal sac compression occurs at the slippage level: while the vertebral body slides forward, posterior elements (spinous process, laminae) remain in place → ventral and dorsal compression → canal narrowing. Foraminal stenosis also occurs because slippage changes foramen dimensions → exiting root is compressed.
Double canal appearance on axial CT at the slippage level where the upper vertebral body and lower vertebral posterior elements appear at the same section. Pathognomonic axial CT finding of spondylolisthesis, named for its resemblance to Napoleon's tricorn hat.
Loss of cortical continuity in the pars interarticularis on CT sagittal reformat and axial sections — diagnostic finding of isthmic spondylolisthesis. Acute defect appears as thin fracture line, chronic defect as wide lysis area with sclerotic margins. Bilateral defect leads to anterior slippage. Unilateral defect is usually stable and may be asymptomatic. Scotty dog sign — pars defect appears as 'collar on the scotty dog' on oblique CT/radiograph.
Report Sentence
Pars interarticularis defect at __[L5/L4] level __[bilaterally/unilaterally] on CT, consistent with isthmic spondylolisthesis.
Anterior slippage of one vertebra relative to the one below and thecal sac compression at this level on sagittal T2-weighted MRI. Degree of slippage determined by Meyerding classification. Disc at slippage level is usually degenerative (T2 signal loss). Thecal sac shows ventral (disc/vertebra pushed forward by slippage) and dorsal (posterior elements remaining in place) compression. Foraminal narrowing is also evaluated.
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Grade __[I/II/III/IV] anterior slippage (Meyerding) of __[L4/L5] over __[L5/S1] on sagittal T2 MRI with thecal sac compression at this level.
Double canal appearance at slippage level on axial CT — Napoleon hat sign. Due to slippage, the upper vertebral body and lower vertebral posterior elements appear at the same axial section → normally single spinal canal appears as two separate structures. This finding is particularly prominent in high-grade slippage and is the characteristic axial CT finding of spondylolisthesis.
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Double canal appearance (Napoleon hat sign) at __[L4-5/L5-S1] level on axial CT, consistent with spondylolisthesis.
Neural foramina narrow at the slippage level: anterior slippage changes craniocaudal and AP dimensions of the foramen → exiting nerve root is compressed. Foraminal fat plane obliteration on T1 sagittal and foramen narrowing on T2 axial are seen. In degenerative spondylolisthesis, disc bulging + slippage together cause foraminal stenosis. In isthmic type, fibrous tissue/callus at the pars defect site may directly compress the nerve root.
Report Sentence
Foraminal stenosis in the __[left/right/bilateral] __[L4-5/L5-S1] neural foramen at the slippage level with exiting nerve root compression.
In active pars stress reaction, focal edema signal (hyperintense) is seen in the pars interarticularis region on STIR/T2 fat-sat sequences. Shows the early (pre-fracture) phase of stress fracture — equivalent to increased uptake on bone scintigraphy. Presents with low back pain in young athletes. Fracture line may not yet be visible on CT. Healing can be achieved with early diagnosis and activity modification.
Report Sentence
Focal bone marrow edema in the __[L5/L4] pars interarticularis region on STIR, consistent with active stress reaction.
Criteria
From facet joint degeneration, pars interarticularis intact, >50 years, female predominant, most common at L4-5
Distinct Features
Most common spondylolisthesis type. Facet sagittalization and degeneration. Usually Grade I-II. Accompanied by advanced disc degeneration
Criteria
Pars interarticularis defect (stress fracture), most common at L5-S1, onset in young athletes, bilateral pars defect
Distinct Features
Repetitive extension + rotation stress (gymnastics, football). CT best demonstrates pars defect. High-grade slippage potential (Grade III-IV), progression risk during growth
Criteria
Congenital facet joint anomaly (hypoplasia/aplasia), usually L5-S1, diagnosed in childhood/adolescence
Distinct Features
Pars interarticularis intact but elongated. High-grade slippage risk. Spina bifida occulta frequently accompanies. Surgical stabilization usually required
Distinguishing Feature
Spinal stenosis shows degenerative canal narrowing without vertebral slippage; spondylolisthesis has vertebral slippage with stenosis predominant at slippage level
Distinguishing Feature
DDD shows disc signal loss and endplate changes, may not have slippage; spondylolisthesis specifically defines vertebral slippage, DDD frequently accompanies
Distinguishing Feature
Facet arthropathy has predominant facet degeneration without slippage; degenerative spondylolisthesis has facet arthropathy with slippage and prominent facet sagittalization
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
6-monthLow-grade (Grade I-II) stable spondylolisthesis responds to conservative treatment (physical therapy, core stabilization, NSAIDs). Surgical indications: high-grade slippage (Grade III+), progressive slippage (instability on dynamic radiographs), refractory radiculopathy, cauda equina syndrome. Surgery is usually decompression + posterolateral fusion. Pars repair may be considered for young athletes with isthmic type. Flexion-extension dynamic radiographs are important for instability assessment (>3-5 mm translation = unstable).
Spondylolisthesis can cause low back pain and radiculopathy. Conservative treatment (physical therapy, core stabilization, NSAIDs) is applied for low-grade (Grade I-II) stable slippage. Surgical decompression + fusion is indicated for high-grade (Grade III-IV) or progressive slippage, nerve root compression, and cauda equina syndrome. Pars repair may be considered for young athletes with isthmic type. Flexion-extension dynamic radiographs are important for instability assessment.