Cranial burst fracture, a severe head injury unique to infants, consists of a widely diastatic (> 4 mm) skull fracture associated with acute extracranial cerebral herniation beneath unbroken scalp.
http://www.ajnr.org/content/21/4/795

http://www.gwpda.org/medical/fracture/Bone.htm

COMPLETE PERFORATIONS. -The projectile that produces them having a sufficient but variable active power to go through the two bony walls, complete perforations are either more or less simple, or else comminuted even excessively comminuted.

In regard to the general direction of the fissures, the limitation of the splinters and the shape of the fragments, fracture by complete perforation nearly always shows much resemblance to fracture by contact with two more or less subdivided large lateral splinters, or to cuneiform V-shaped fractures (Fig. 11, 1 and 2).

The bony aperture of entry is circular and regular, of the same dimensions as the projectile, or smaller, occasionally oval in shape. The bony aperture of exit is variable in form. Rarely circular and regular, it is nearly always, owing to loss of substance, more or less quadrilateral, its borders being formed by the splinters that the projectile has detached (fig. 11, 3 and 4). These splinters, more or less free, are then stationary; they can, however, be thrown off.

In such an instance the bullet has not acted alone, as in a contact fracture or in perforation of only one bony wall. The splinters it has torn off at the aperture of entry, the subdivided splinters close to the track to which the bullet has communicated part of its active power, the fragments of the bullet which may have broken in pieces, have all acted as secondary projectiles. These last, propelled towards the bony aperture of exit in a more or less irregular manner, have increased the damage, and have given rise in some cases to a ****fracture feeling like a bag of nuts****; even in some instances the seat of fracture has been freed from splinters (focus swept away, bullet fired from a very short distance-- Fig. 11, 5)