A radiological study on the drug diffusion of two approaches of quadratus lumborum block: a randomized trial

Perioperative analgesia of the anterior quadratus lumborum block at the supra-arcuate ligament (QLB-LSA) and transmuscular quadratus lumborum block (TMQLB) has been reported. However, no studies have compared their radiological local anesthetic diffusion patterns. This study aimed to evaluate and compare the diffusion characteristics of these two approaches.

Ninety-eight patients undergoing CT-guided hepatic microwave ablation under intravenous anesthesia were randomized to the QLB-LSA group or the TMQLB group, both groups received an injection of a mixture of 0.375% ropivacaine and iohexol (30 mg/mL) bilaterally. Drug spread to the T12 vertebral level and above on CT was defined as cranial diffusion, and that below T12 was defined as caudal diffusion. The primary endpoint was the number of vertebral segments with cranial diffusion between groups, and drug distribution was recorded via CT and 3D-CT.

QLB-LSA had significantly greater bilateral cranial diffusion than TMQLB (both sides, P<0.001), while TMQLB had markedly greater bilateral caudal diffusion (both sides, P<0.001). QLB-LSA diffused cranially to T6, predominantly in the thoracic sympathetic nerve chain, thoracic paravertebral spaces (TPVS), and intercostal spaces. Caudally, it distributed to the L1 psoas major, quadratus lumborum muscle, and L1-3 anterior thoracolumbar fascia layer (ATLF). TMQLB only diffused cranially to T10 (same cranial distribution as QLB-LSA) and rarely reached the L1 psoas major caudally; instead, it was predominantly distributed in the L1-4 quadratus lumborum and ATLF.

QLB-LSA achieved superior cranial diffusion compared with TMQLB, while TMQLB favored caudal diffusion. Both techniques showed cranial distribution in the thoracic sympathetic nerve chain, TPVS, and intercostal spaces, with caudal distribution mainly in the thoracolumbar fascia spaces.