Grynfeltt–Lesshaft hernia is a herniation of abdominal contents through the back, specifically through the superior lumbar triangle, which is defined by the quadratus lumborum muscle, twelfth rib, and internal oblique muscle.
Grynfeltt described a hernia through the superior lumbar triangle in 1866 (Grynfeltt, 1866). In 1870, Lesshaft independently reported a similar case (Lesshaft, 1870).