Figure 43-6 Anatomic variants of sacrum and sacral hiatus. Sacral hiatus variants. A, Normal. B, Longitudinal slitlike hiatus. C, Second midline hiatus. D, Transverse hiatus. E, Large hiatus with absent cornua. F, Transverse hiatus with absent coccyx and two prominent cornua and two proximal "decoy hiatuses lateral to the cornua." G–I, Large midline defects contiguous with sacral hiatus. J–L, Enlarged longitudinal hiatuses, each with an overlying decoy hiatus. (From Willis RJ: Caudal epidural block. In Cousins MN, Bridenbaugh PO [eds]: Neural Blockade in Clinical Anesthesia and Management of Pain, 2nd ed. Philadelphia, JB Lippincott, 1988, p 365.)