Occipital twins are joined at the occipital lobe in the back of the head and vertical are joined on the top of the head and usually face opposite directions. The junctional diameter is often smaller in partial forms and occasionally an incomplete layer of bone may be present between the twins. Each child maintains independent calvarial convexities except at the common area of skull junction. The dura of both children may be intact or deficient and cortical gyri may interdigitate. Additionally, shared dural venous sinuses is usually absent, or, if it is present, negligible. These twins usually undergo successful separation and both twins may live to lead normal lives. Gestation and embryology
The exact nature of how conjoined twins develop in utero remains unclear. Embryologists have traditionally attributed identical twinning as "splitting or fission" of either the inner cell mass of pleuripotential cells or early embryonic disc at 13–14 days of gestation just before the primitive streak. Some theorists suggested that conjoined twins develop as a result of the failed fusion of a single fertilized ovum. However a new hypothesis suggests that cranial fusion occurs between two separate embryos before the end of the 4th week of gestation. This can happen because the cranial neuropore is still open, which is responsible for the ultimate fusion and formation of the brain stem and central nervous system. Furthermore, this secondary fusion of embryonic discs could implicate that intact skin will not fuse to other intact skin, including the ectoderm of the embryo.
Partial CPT was defined as "lacking substantial shared dural venous sinuses", whereas total CPT "share a large portion of their dural venous sinuses and present with pronounced brain compression, which leads to distortion within the cranium". Total
Total craniopagus twins share a large portion of dural venous sinuses and present with pronounced brain compression, leading to distortion within the cranium. Stone and Goodrich also defined two main subtypes, based on whether the long-axis angle between the twins was angular or vertical. The angular subtype has a higher rate of comorbidities than the vertical subtype.Vertical craniopagus calvaria is continuous and is further subdivided on the basis of intertwin axial facial rotation:

Type 1: both children face in the same general directional axis so that the angle between twins is less than 40 degrees. These twins show relatively symmetric superior bi-parietal or vertex compressional flattening. Type 2: both children face opposite directions so that the deformity shows an axial rotation between 140 and 180 degrees.