Dura mater
The dura mater (dura mater encephali) is the outermost, strongest, and densest protective layer. An essential topographical feature of this structure lies in the varying nature of its attachment to the surrounding bones. It adheres quite loosely to the bones of the cranial vault, whereas it is fused extremely tightly with the internal cranial base.
Anatomically, this sheet is easily split into two due to the loose connection between its own layers. The superficial layer of the dura mater possesses high tensile strength, which is why surgeons often use it as a patch material for closing various defects.
Two important clinical spaces are adjacent to the dura mater:
- Epidural space is located between the cranial bones and the dura mater. Under normal physiological conditions, this space does not exist. It forms exclusively under pathological conditions, when blood begins to accumulate due to bone damage and blood vessel rupture. Such an accumulation is called an epidural hematoma.
- Subdural space is a narrow cleft between the dura mater and the arachnoid mater. This is the typical site for the formation of subdural hematomas. This cleft is not isolated: it has a direct communication with the analogous subdural space surrounding the spinal cord, and also transitions into the perineural spaces of the cranial nerves.
Arachnoid and pia mater
The arachnoid mater (arachnoidea encephali) is the middle, thin layer. Its distinctive feature is that it bridges across the cerebral sulci, forming characteristic bridges, but never extends deep into the sulci themselves. Externally, it is separated from the dura mater by the subdural cleft, and internally, by the subarachnoid space.
The pia mater (pia mater encephali) is the deepest layer. It is exceptionally vascular. Unlike the arachnoid mater, the pia mater closely adheres to the brain tissue and penetrates into absolutely all of its sulci. In addition, the vascular network of this membrane enters the cavities of the third (III) and fourth (IV) cerebral ventricles, where it takes direct part in the formation of their choroid plexuses.
Subarachnoid space and cisterns
Subarachnoid space, or subarachnoid space, is located between arachnoidea and pia mater. Its main content is cerebrospinal fluid (CSF). This space freely communicates with the subarachnoid space of the spinal cord and the ventricular system of the brain. On the basal surface of the brain (base of the brain), this space forms characteristic dilations — cisterns.
| Space | Localization | Contents (normal) | Clinical significance |
|---|---|---|---|
| Epidural | Between the skull and the dura mater | Absent | Site of epidural hematoma accumulation |
| Subdural | Between the dura mater and arachnoidea | Cleft-like | Site of subdural hematoma accumulation |
| Subarachnoid | Between the arachnoidea and pia mater | Cerebrospinal fluid | Site of cistern formation |
Key cisterns of the subarachnoid space:
- Cerebellomedullary cistern (cisterna cerebellomedullaris). Located in the deep cleft between the cerebellum and the medulla oblongata, at the level of the upper edge of the atlanto-occipital membrane. This is a very large reservoir of CSF, the depth of which can reach 1.5 cm. Inferiorly, the cistern transitions into the subarachnoid space of the spinal cord, and superiorly communicates with the cavity of the IV ventricle. From there, CSF can move through the cerebral aqueduct (Sylvian aqueduct) into the III ventricle, which, in turn, communicates with the lateral ventricles. It is at this location that physicians perform suboccipital puncture for diagnostic or therapeutic purposes.
- Chiasmatic cistern (cisterna chiasmatis). Located anterior to the optic chiasm (chiasma opticum). From a clinical standpoint, this site is extremely important: an inflammatory process—optochiasmatic arachnoiditis—can develop here, a formidable symptom of which is progressive vision loss.
Briefly: answers to topical questions
Which specific blood vessels are most frequently damaged and serve as the source of bleeding during the formation of an epidural hematoma?
The source of bleeding in the formation of an epidural hematoma is most often meningeal vessels, primarily the middle meningeal artery. Bleeding can also originate from the following structures:
- Middle meningeal artery — the largest meningeal vessel, the rupture of which often accompanies cranial bone fractures (especially in the temporal region).
- Diploeic veins — damaged in fractures of the cranial vault bones.
- Pachymeningeal granulations — their damage can also cause blood accumulation in the epidural space.
What dural folds are formed by the dura mater, separating different parts of the brain?
The dura mater forms folds that penetrate between the cerebral hemispheres and separate its parts. These include:
- Falx cerebri (falx cerebri) — a vertical plate separating the cerebral hemispheres.
- Tentorium cerebelli (tentorium cerebelli) — a horizontal plate separating the occipital lobes of the cerebrum from the cerebellum.
- Falx cerebelli (falx cerebelli) — separates the cerebellar hemispheres.
- Diaphragma sellae (diaphragma sellae) — a plate covering the sella turcica and superiorly bounding the receptacle for the pituitary gland.
Which subarachnoid cisterns are located on the basal surface of the brain?
On the basal surface of the brain, expansions of the subarachnoid space form the following cisterns:
- Cerebellomedullary cistern (cisterna cerebellomedullaris) — the largest, located between the posterior border of the cerebellum and the medulla oblongata.
- Interpeduncular cistern (cisterna interpeduncularis) — located between the cerebral peduncles.
- Chiasmatic cistern (cisterna chiasmatis) — located anterior to the optic chiasm.
- Cistern of the lateral fossa of the cerebrum (cisterna fossae lateralis cerebri) — located in the fossa of the same name.
Through which anatomical structures does the outflow of cerebrospinal fluid from the subarachnoid space into the venous sinuses occur?
The outflow of cerebrospinal fluid from the subarachnoid space into the venous sinuses occurs through arachnoid villi:
- Arachnoid granulations (granulationes arachnoideales), or Pachydermic/Pacchionian granulations. They project into the lumen of the dural venous sinuses; CSF resorption into the venous sinuses occurs through them.
What external anatomical landmarks does a surgeon use to perform a suboccipital puncture?
To perform a suboccipital (cisternal) puncture, the surgeon uses the bony prominences of the occipital bone and cervical spine. The external anatomical landmarks are:
- External occipital protuberance (protuberantia occipitalis externa).
- Spinous process of the second cervical vertebra (axis).
The needle insertion point is located strictly on the midline, at the midpoint of the distance between these two anatomical structures.
To remember the sequence of the meninges from outside to inside, the phrase is used: "Dura Arachnoid Pia" (Dura mater, Arachnoid mater, Pia mater).
Class and exam questions
How does the epidural space differ from the subdural space?
The epidural space is located between the cranial bones and the dura mater; normally it is absent and appears only upon blood accumulation. The subdural space is a permanently existing cleft between the dura mater and the arachnoid mater.
Does the arachnoid mater enter the cerebral sulci?
No, the arachnoid mater passes superficially over the cerebral sulci without penetrating into them. Only the pia mater extends into all the sulci.
Where is the suboccipital puncture performed?
Suboccipital puncture is performed at the level of the upper edge of the atlanto-occipital membrane, with the needle entering the cerebellomedullary cistern (cisterna cerebellomedullaris).
What complication is characteristic of inflammation in the chiasmatic cistern?
Inflammation in the region of the cisterna chiasmatis causes optochiasmatic arachnoiditis, which is accompanied by vision loss due to optic nerve damage.
What else to study on this topic
- Topography of the facial nerve canal and its relationship with the tympanic cavity
- Formation of the choroid plexuses in the cerebral ventricles
- Outflow pathways and circulation of cerebrospinal fluid (CSF)
- Surgical anatomy of the mastoid process and mastoid antrum (antrum mastoideum)
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