Figure-1.

Type Ir PPB is characterized by multicystic structures where the septa lack the characteristic small primitive cells underneath the epithelium (a, b). In contrast, type I PPB is characterized by the presence of these small primitive cells which can either present as a continuous or discontinuous growth pattern (c, d, e, f). In more than half of the cases the primitive cells underneath the epithelium are rhabdomyoblasts, and a classic association with immature island of cartilage is seen in PPB regardless of type (c, d). Occasionally the cystic septa are expanded by the immature cells, a possible sign of early progression to type II (e, f).