Anatomical Variations of the Lumbosacral Plexus
Anatomical variations of the lumbosacral plexus are extremely common, occurring in approximately 41-50% of individuals based on cadaveric dissection studies.
Prevalence of Variations
The frequency of anatomical variants in the lumbosacral plexus is substantial and clinically significant:
- Overall variation rate ranges from 41-50% when examining the entire lumbosacral plexus complex 1
- Lumbar plexus variations occur in approximately 20% of individuals on average, with individual nerve variations ranging from 8.8% to 47.1% depending on the specific nerve examined 2
- Sacral plexus variations were documented in 41 of 100 examined plexi (41%) in one comprehensive cadaveric study 1
Specific Common Variations
Lumbar Plexus Variations
The most frequently encountered anatomical variants include:
- Double ascension of the L4 root from the intervertebral foramen occurs in 25% of cases, with plexiform ascension in an additional 5% 1
- Lateral femoral cutaneous nerve variations occur in up to 47.1% of cases, representing the highest variation rate among lumbar plexus branches 2
- Accessory obturator nerve is present in approximately 12% of individuals 3
- Absence of the iliohypogastric nerve occurs in a small percentage of cases 2
- Early bifurcation of the genitofemoral nerve into genital and femoral branches is commonly observed 2
Sacral Plexus Variations
- Double ascension of the L5 root occurs in 8% of cases, with plexiform ascension in 4% 1
- Double S1 root at ascension from sacral foramina is present in 16% of cases 1
- Double S2 root occurs in 8% of cases 1
- Thickened lumbosacral trunk is observed in 19% of individuals 1
Clinical Implications
These variations have direct clinical relevance:
- Anatomical variations can complicate regional anesthesia techniques, particularly lumbar plexus blocks, as the relationship between nerve branches and the psoas muscle varies 3
- Nerve entrapment syndromes may result from anatomical variants, such as piriformis syndrome where the sciatic nerve is compressed due to anatomic variation 4
- Surgical planning requires awareness of these variations to avoid iatrogenic nerve injury during pelvic and spinal procedures 1
- MRI interpretation must account for normal anatomical variants to avoid misdiagnosis of pathology 5
Important Caveats
- The reported prevalence of specific variations shows wide discrepancies across studies 2, likely due to differences in dissection techniques, sample sizes, and classification systems
- Bilateral symmetry cannot be assumed, as variations may be unilateral 1
- The presence of anatomical variations does not necessarily correlate with clinical symptoms unless compression or entrapment occurs 4