Bat sign in interspinous view for lumbar neuraxial ultrasound

• The articular processes form the bat's ears.
• The posterior complex (ligamentum flavum, posterior epidural space, and posterior dura) forms the top of the bat's head.
• The transverse processes appear with an upward tilt that forms the bat's wings.
• The anterior complex (posterior longitudinal ligament/vertebral body) forms the bottom of the bat.

For further detail refer to UpToDate content on neuraxial ultrasound for anesthesia.