What are the treatment options for suspected transitional anatomy on lumbar MRI (Magnetic Resonance Imaging)?

Management of Suspected Transitional Anatomy on Lumbar MRI

When transitional anatomy is suspected on lumbar MRI, the primary treatment approach is conservative management with observation, as these anatomical variants are common (present in approximately 24% of the population) and often asymptomatic, requiring intervention only when definitively linked to pain through diagnostic injections. 1, 2

Initial Diagnostic Confirmation

Accurate Vertebral Identification

• Use whole-spine imaging or anatomical landmarks to confirm vertebral numbering, as misidentification can lead to wrong-level surgery 2, 3
• The iliolumbar ligament (ILL) emerges from L5 or the adjacent disc in 93.8% of normal cases and serves as a reliable marker for L5 identification 3
• Costal facets at T12 are present in 96.9% of normal cases, helping identify the thoracolumbar junction 3
• Measure the A-angle (line parallel to sacral superior surface versus perpendicular to scan table): values >39.8° predict lumbosacral transitional vertebra (LSTV) with 80% sensitivity and 80% specificity 4
• Vascular landmarks (aortic bifurcation, IVC confluence, renal arteries) show variable positioning and shift cranially with sacralization or caudally with lumbarization 3, 5

Classification and Morphology Assessment

• Apply the Castellvi classification system on coronal images to categorize LSTV types (I-IV based on transverse process morphology) 1, 2
• Evaluate sagittal and axial CT images when available, as Castellvi type-III LSTV (most common at 37.8%) demonstrates S2-like features on axial images despite being labeled as L5 2
• Recognize that 78.4% of LSTV cases coexist with thoracolumbar transitional vertebrae (TLTV), most commonly at T13 2

Treatment Algorithm

Conservative Management (First-Line)

• Initiate conservative treatment for all patients with suspected symptomatic LSTV, as surgical intervention is reserved only for treatment failures 1
• Conservative measures include physical therapy, NSAIDs, and activity modification 1
• The majority of patients with transitional anatomy remain asymptomatic and require no specific treatment 1, 2

Diagnostic Confirmation of Pain Source

• Perform diagnostic local anesthetic injections at the pseudoarticulation (the "false joint" between transverse process and sacrum) to confirm LSTV as the pain generator 1
• Obtain radionuclide bone scan to identify increased uptake at the transitional segment, which combined with positive injection response confirms symptomatic LSTV (Bertolotti's syndrome) 1
• This two-step diagnostic approach is essential because low back pain is common (affecting general population) and LSTV prevalence is high (12.6-23.8%), making coincidental findings frequent 1, 2

Surgical Intervention (Highly Selective)

• Reserve surgical resection exclusively for patients who fail conservative treatment AND have definitively confirmed pain from the pseudoarticulation through positive diagnostic injections 1
• Surgical options include resection of the anomalous transverse process or fusion, but evidence for effectiveness remains limited 1
• Types II and IV LSTV show stronger association with low back pain due to pseudoarticulation susceptibility to arthritic changes and osteophyte formation causing nerve root entrapment 1

Critical Clinical Pitfalls

Surgical Planning Considerations

• Always obtain whole-spine imaging or use multiple anatomical landmarks before any spinal surgery to prevent wrong-level procedures 2, 3
• Standard AP radiographs and isolated lumbar MRI frequently misidentify transitional vertebrae 1, 3
• Three-dimensional CT imaging provides superior detection of transitional vertebrae compared to conventional imaging 2

Measurement Accuracy

• Recognize that spinopelvic parameters (pelvic incidence, lumbar lordosis) may be inaccurate in patients with LSTV, affecting surgical planning 2
• The lumbosacral transitional anatomy of Castellvi LSTV resembles normal L5-S1 on sagittal images, while S6 LSTV (6 sacral vertebrae) resembles normal S1-S2 2

Avoiding Overtreatment

• Do not attribute all low back pain to incidentally discovered LSTV without confirmatory diagnostic testing 1
• The high prevalence of both conditions necessitates rigorous exclusion of other pain sources (disc herniation, facet arthropathy, spinal stenosis) before attributing symptoms to transitional anatomy 1
• Further research with larger sample sizes and longer follow-up is needed to better demonstrate surgical effectiveness 1