Pneumocephalus

Excerpt

The skull or cranium is the skeleton of the head, consisting of 2 parts: the neurocranium and the facial skeleton (see Image. Skull Interior). The neurocranium or cranial vault protects the meninges and brain. The calvaria or skullcap serves as the brain's roof, while the cranial base acts as the floor. The cranial base is divided into the anterior, middle, and posterior cranial fossae (see Image. Skull Base and Foramina).

The neurocranial bones include the following:

1. Frontal bone

2. Paired parietal bones

3. Paired temporal bones

4. Occipital bone

5. Sphenoid bone

6. Ethmoid bone

The scalp overlies the calvaria from the occipital bone's superior nuchal lines to the frontal bone's supraorbital margins anteriorly and the zygomatic arches' temporal fascia laterally (see Image. Relationship of the Meniges to the Skull and Brain). The 5 layers of the scalp are best remembered by the acronym "SCALP": skin, connective tissue (dense), aponeurosis, loose connective tissue, and pericranium.

The meninges lie deep to the skull's endosteal layer. The 3 meningeal layers, from superficial to deep, are the dura (dura mater), arachnoid (arachnoid mater), and pia (pia mater). The meningeal spaces from superficial to deep are the following:

1. Epidural: a potential space that can form in the skull-dura interface; also known as the extradural space

2. Subdural: a potential space that can develop between the dura and subarachnoid

3. Subarachnoid: an actual space between the arachnoid and pia that contains blood vessels, cerebrospinal fluid (CSF), and trabecular cells

The facial skeleton, also known as splanchnocranium or viscerocranium, comprises the skull's anterior segment. The bones of the facial skeleton are the following:

1. Paired lacrimal bones

2. Paired nasal bones

3. Paired maxillae

4. Paired zygomatic bones

5. Paired palatine bones

6. Paired inferior nasal conchae

7. Mandible

8. Vomer

Pneumocephalus, also known as pneumatocele or intracranial aerocele, is the presence of air in the epidural, subdural, or subarachnoid space or within the brain parenchyma or ventricular cavities. Lecat first described this condition in 1741 but Luckett coined the term "pneumocephalus" independently in 1913. Wolff used the same term to describe the condition in 1914. The term "tension pneumocephalus" was proposed in 1962 by Ectors, Kessler, and Stern (see Image. Tension Pneumocephalus).

Pneumocephalus can occur spontaneously or as a complication of trauma and cranial surgery. This condition is classified as simple or tension pneumocephalus, depending on severity and progression. Pneumocephalus can also be acute or delayed based on the onset. Acute pneumocephalus develops less than 72 hours before presentation, while the delayed type develops more than 72 hours after presentation.

Pneumocephalus has to be differentiated from the following terms:

1. Pneumorrhachis, which denotes intraspinal air

2. Pneumocele, which is a focal or diffuse paranasal sinus (usually frontal) enlargement with bone thinning and hyperpneumatization

3. Pneumosinus dilatans, which is the same as a pneumocele but has the sinus walls intact and normal

4. Pneumoventricle, which is the presence of intraventricular air

The term "tension pneumoventricle" is used when air accumulates in the ventricles, increasing the intracranial pressure (ICP) and potentially compressing the brain's vital centers (see Image. Pneumocephalus and Pneumoventriculi).