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The subdural space interpreted as a cellular layer of meninges.

The subdural region within the cranial meninges is examined in guinea pigs by electron microscopy. The fine structures of the arachnoid membrane and dura are described separately in specimens that have been isolated from each other during removal from the cranial cavity. In addition, the fine structure of the intact dura-arachnoid is described, where the subdural space would be present in an undisrupted state. Lastly, the inner surface of the dura and the outer surface of the arachnoid membrane are examined at the point of separation between the two specimens where the dura is reflected from the arachnoid by experimental dissection. From these observations morphologic criteria are established for identifying the constituents and boundaries of the subdural space and for explaining mechanisms in the histogenetic process of "opening" or enlarging this space. The morphologic identity of the classic subdural space is reinterpreted in light of the findings. The subdural space, traditionally described as a fluid-filled potential cavity existing in an extracellular compartment, is not apparent in the guinea pig. Instead, fragile cells designated as light cells occupy the compartment between the dura and arachnoid, with very little extracellular space available. Experimental opening of the subdural space occurs, significantly, along pathways extending by fracture through the cytoplasm and intercellular separation of these light cells rather than by enlargement of a preexisting mesothelial-lined intercellular space between these cells and the true arachnoid cells. Cytoplasmic fine structure of light cells suggests a close kinship with cells in the meningeal layer of the dura. The functional significance of the light cells and their possible role in subdural hematomas is discussed.

Animals

On the question of a subdural space.

The structure of the meninges, with particular attention to the architecture of the inner portions of the dura mater and the arachnoid mater, has been reviewed in reference to the probable existence of a "subdural" space. The dura is composed of fibroblasts and large amounts of extracellular collagen. The innermost part of the dura is formed by the dural border cell layer. This layer is characterized by flattened cells with sinuous processes, extracellular spaces containing an amorphous material, and the presence of junctions between its cells. The dural border cell layer is continuous with the inner (meningeal) portions of the dura and may be attached to the underlying arachnoid by an occasional cell junction. The arachnoid consists of an outer part, the arachnoid barrier cell layer, and an inner portion, the arachnoid trabeculae which bridge the subarachnoid space. Arachnoid barrier cells are electron-lucent, closely apposed to each other, and joined by many cell junctions; in this layer there is little extracellular space and essentially no intercellular material. Arachnoid trabecular cells cross the subarachnoid space in a random manner, have extracellular collagen associated with their flattened processes, and form structures of variable shapes and sizes. There is no evidence of an intervening space between the arachnoid barrier cell layer and the dural border cell layer that would correlate with what has been called the subdural space. When a tissue space is created in this general area of the meninges it is the result of tissue damage and represents, in most instances, a cleaving open of the dural border cell layer. In this situation, extracellular spaces in the dural border cell layer are enlarged, cell junctions are separated, and it is probable that cell membranes are damaged. A survey of reports describing the morphology of the inner and outer capsule of so-called subdural hematomas in humans reveals that dural border cells are found in both parts of the capsule. Also, experimental infusion of blood into this portion of the meninges in animals frequently dissects open the dural border cell layer. These data support the view that what has been called a subdural hematoma is most frequently a lesion found within the layer formed by dural border cells. It is suggested that the so-called subdural space is not a "potential" space since the creation of a cleft in this area of the meninges is the result of tissue damage. In this respect it shares no similarities with legitimate potential spaces (i.e., serous cavities) found at other locations in the body.(ABSTRACT TRUNCATED AT 400 WORDS)

Arachnoid

Injection into the extra-arachnoid subdural space. Experience in the treatment of intractable cervical pain and in the conduct of extradural (epidural) analgesia.

The anatomy and radiological appearances of the subdural space in the cervical region are described. Recognition of this space facilitates neurolytic injections for severe cancer pain in the distribution of the cervical nerve roots. The subdural space may have significance also in explaining the extensive sensory block which follows a delayed or 'massive' lumbar extradural injection.

Analgesics

[Electron microscopic study of the process of the removal of autogenous blood erythocytes beyond the limits of the subdural space].

The internal plate of the dura mater and arachnoidea of the dob brain was studied by electron microscopy after introducing 0.3--0.5 ml of the autogenous blood into the subdural space. The arachnoidea of the excretory channels and structural elements of the internal plate of the dura mater (cells of the internal covering layer, the collagen fibril and microfibril layer, the wall of the blood capillaries of the internal capillary network) involve the morphological substratum of the liquor-blood barrier-I between the liquor and blood of the blood capillaries of the internal capillary network of the dura mater. It was established that red cells of the subdural space penetrate the thickness of the dura mater, where they concentrate around blood capillaries of the internal capillary network, rather than penetrate into the arachnoidea.

Animals

Histological reaction to various conductive and dielectric films chronically implanted in the subdural space.

Thirty different test patches of various thin film materials were chronically implanted in the subdural space of cats to determine their suitability as components for proposed neuroprosthetic devices. In particular, materials employed by the microelectronics industry were screened, and reactions were found to be quite dependent on specific formulations or surface preparations of otherwise similar materials. A nonspecific but severe complication of pressure necrosis under thin films that spontaneously roll and curl in vivo was noted.

Animals

Tension pneumocephalus of the cranial subdural space: a case report.

A case of subdural tension pneumocephalus is presented. Computerized cranial tomography permitted rapid diagnosis including localization of the air, thus facilitating prompt treatment. Tension pneumocephalus should be considered in a patient with a cerebrospinal fluid drainage device who deteriorates after craniotomy.

Aged

The subdural space: the third place to go astray.

Subdural placement of the tip of the Tuohy needle or epidural catheter may account for many unexpected complications of attempted epidural blockade, for example, 'unexplained' headache, false-negative aspiration test down needle or catheter, false-negative test dose, unilateral block, delayed total spinal and neurological sequelae, as well as profound block of delayed onset that is characteristic of subdural blockade. Cases are reported in support of this hypothesis.

Adult

Expansion of an air-filled subdural space during nitrous oxide anesthesia.

The long-term administration of nitrous oxide anesthesia during craniotomy as well as following closure of the parietal craniotomy flap (under no tension) leads to significant expansion of the residual air bubble trapped under the dura. A case is presented in which an extracerebral avascular space, filled only with gas, caused a marked shift of the intracranial structures and uncal herniation secondary to nitrous oxide anesthesia during craniotomy and postcraniotomy angiography.

Adult

[Supravermian subdural triangle limited by the veins of the posterior fossa. Normal radio-anatomical study. Vermis herniation in the supravermian subdural space or superior vermis herniation].

The author describes a conical sub-dural space above the vermis limited in front by Galien's ampulla, behind by the right venous sinuses and, below by the superior cerebellar vein. This space, which is not filled with air injected by the cisternal route, is only shown in lateral views thanks to its venous outlines. In cases of raised intracranial pressure, the superior cerebellar vermis may occupy this space so that a sort of impaction occurs at this level, which the author proposes calling smaller than superior vermial impaction greater than. Among forms of cerebral herniation, vermial impaction may not occur when the CSF obstruction occurs at another level.

Cerebellar Diseases

A spinal haematoma occurring in the subarachnoid as well as in the subdural space in a patient treated with anticoagulants.

A 75-year-old man on anticoagulant therapy suddenly experienced an excruciating back pain and subsequently developed a paraplegia. At operation a subarachnoid and a subdural haematoma were found, extending between the levels of the vertebrae T3 and L2. This extremely rare combination of haematomas may have been caused either by rupture of a small vessel in the arachnoid membrane or by rupture of the arachnoid membrane itself, secondary to a massive haemorrhage in the subarachnoid space.

Aged

Accidental subdural catheterization: radiological evidence of a possible mechanism for spinal cord damage.

We describe the inadvertent subdural insertion of a lumbar extradural catheter in a primiparous woman in labour. A small quantity of local anaesthetic resulted in extensive motor and sensory block. Computed tomography performed after contrast injection demonstrated unequivocally that the catheter was in the subdural space. The catheter and injected fluid produced considerable displacement of the arachnoid within the thecal sac. We postulate that this could result in arterial compression or direct damage to the spinal nerve roots. Such a mechanism might explain some of the cases of permanent neurological damage associated with extradural analgesia.

Adult