Neuroanatomy Draw It To Know It

24 Neuroanatomy: Draw It to Know It

Hemorrhages & Innervation (Advanced)

Here, let’s learn a few important clinical correlates to the
meninges. First, let’s learn how to distinguish epidural
and subdural hematomas (Fig. 2-2 ). In epidural hema-
toma, blood collects between the periosteal dura and
skull. As it collects, it pushes aside the spong y brain
parenchyma and forms a biconvex lens-shaped fl uid col-
lection with one side of the convexity displacing brain
matter and the other side layering against the cranium.
In subdural hematoma, blood collects within the dural
border cell layer, external to the underlying arachnoid
layer. Th e dural border cell layer is less resistant than the
brain tissue, so blood spreads along the border cell layer
in a crescent shape.
Next, let’s distinguish these two hematoma types
based on whether or not they respect the dural folds.
Epidural hematomas form external to the periosteal sub-
layer, and therefore, they are unaff ected by the dural
folds (the falx cerebri, tentorium cerebelli, and falx cere-
belli), which lie deep to them. On the contrary, subdural
hematomas form underneath the meningeal sublayer
and pool at the site of the dural refl ections: they do not
cross the dural folds.
Lastly, consider the eff ect of the cranial sutures (the
junctions between the skull bones) on both types of
hematoma. Because epidural hematomas lie between the
dura and skull, they are stopped at the cranial sutures; in
contrast, subdural hematomas lie underneath the dura
mater and are unaff ected by the cranial sutures.^18 , 19
Figures 2-3 and 2-4 , each contain subarachnoid hem-
orrhage; the subarachnoid space was described in the
previous lesson — CISTERNS, SINUSES, & VEINS.

Next, let’s consider the innervation pattern of the

meninges. Most meningeal innervation comes from the

trigeminal nerve, which innervates the supratentorial

meninges, including the meninges of the anterior and

middle cranial fossae. Posterior cranial fossa meningeal

innervation is derived, most notably, from the second

and third cervical spinal nerves and a minor branch of

the vagus nerve. Note that the facial and glossopharyn-

geal nerves potentially play a role in meningeal innerva-

tion, as well.^8 , 11

FIGURE 2-2 Subdural hematoma on left side of page (right side of brain)

and epidural hematoma on right side of page (left side of brain).