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The scalp of the newborn and child is thinner than that of the adult, contains less fat tissue, and is more elastic, but is more susceptible to blunt impacts and to tearing forces. Erythema and pressure marks are relatively uncommon, making it easy to overlook the

Table 20.1. Head circumferences of children. Sources: Altman and Dittmer 1962; Prader and Budliger 1977; Dekaban 1977

Age

Head circumference (cm)

Males

Females

Birth

35.3 (33.5-37.0)

34.7 (33.4-36.0)

0.25 years

40.9 (39.2-42.1)

40.0 (38.5-41.7)

0.5 years

43.9 (42.7-45.4)

42.8 (41.4-44.5)

0.75 years

46.0 (44.5-47.1)

44.6 (43.2-46.3)

1 year

47.3 (45.5-48.4)

45.8 (44.3-47.7)

1.25 years

48.0 (46.3-49.2)

46.5 (44.9-48.4)

1.5 years

48.7 (47.0-49.9)

47.1 (45.5-49.0)

2 years

49.7 (48.0-51.0)

48.1 (46.4-50.1)

2.5 years

50.2 (48.5-51.6)

48.8 (47.0-50.8)

3 years

50.4 (48.9-51.9)

49.3 (47.5-51.1)

effects of blunt force impact by external macroscopic inspection alone (i.e., without autopsy). A special type of injury seen in the newborn infant is massive subgaleal hematoma, sometimes associated with skull fractures. The time-dependent morphological alterations of subcutaneous or subgaleal hematomas may differ from that of comparable injuries in adults (Gonzales et al. 1954; Wilson 1977).

The neonatal skull is characterized by open sutures between the cartilaginous bone plates. Because the cartilaginous skull, especially the cranial vault, ossifies only gradually over the first 2 years of life, the infant skull retains an enormous elasticity. The circumference of the head/skull increases with that of the brain (Fig. 20.2, Table 20.1) and thus is dependent upon age. The fontanels close at different ages (Peacock 1986):

— The posterior fontanel: 2nd postnatal month

— The anterior fontanel: between the 7th and 19th postnatal months (90% of the cases - Aisenson 1950)

The neonatal dura has a structure (Friede 1989) distinct from that of the adult meningeal membrane. The arachnoid granulations do not attain their final form until adulthood, nor do the bridging veins, which display an age-related difference in elasticity (Yamashima and Friede 1984; Friede 1989). A comparative prospective study has shown that so-called subdural neomembranes unassociated with MBI or different types of delivery are common in infants (Rogers et al. 1998).

The outer surface of the arachnoid membrane is fused with the inner surface of the dura mater in a manner which confers scant cohesion at the interface

-months--years-

Fig. 20.2. Head circumference of boys. Source: Nellhaus 1968

-months--years-

Fig. 20.2. Head circumference of boys. Source: Nellhaus 1968

layer, the dura separating easily from the arachnoid. Upon disruption of the interface layers, some cells remain on the surface of the arachnoid and some on the dura mater. Proliferation of these residual cells produces neomembranes. Stretching and tearing of the bridging veins are partly responsible for subdu-ral hemorrhages, the walls of bridging veins in infants being particularly thin (Friede 1989). Moreover, in children the dura tends to develop hygroma or is involved in the process of growing skull fractures as well as leptomeningeal cysts (see below).

Table 20.2. Brain mass before birth in relation to gestational age. Sources: Gruenwald and Minh 1960; Schulz et al. 1962; Guihard-Costa and Larroche 1990

Gestational age (weeks)

Gruenwald and Minh (1960)

Schulz et al (1962)

Guihard-Costa and Larroche (1990)

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