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General paresis combines progressive mental deterioration with a characteristic disorder of speech, fine movement and motor control. The historical phrase “general paralysis of the insane” does not mean complete, simultaneous immobility of every muscle.

Early changes may include impaired judgment, forgetfulness, altered personality, irritability, inappropriate confidence and loss of ordinary social restraint. Expansive or grandiose delusions are characteristic in some cases, but depression, suspiciousness or less spectacular cognitive failure can occur. Increasing dementia and reduced insight are more fundamental than any one extravagant belief.

The physical examination may disclose hesitating or slurred articulation, tremulous lips and tongue, facial tremor, deteriorating handwriting and impaired coordination of the hands. Gait becomes unsteady and weakness advances. Unequal or abnormally reacting pupils, altered reflexes and seizures may occur. Later disease can bring severe cognitive incapacity, swallowing difficulty, incontinence and dependence. Mental and motor manifestations need not develop in a fixed order or with equal severity.^[ref]

The name general paresis was already advocated in a January 1864 pathological study to avoid the ambiguity of “general paralysis.”^[ref] Modern medicine recognises the classical disease as a form of neurosyphilis, involving chronic injury to the brain. This causal diagnosis should be separated from the historical clinical label; it was not securely established by the wording of an 1864 examination. Syphilis serology, relevant cerebrospinal fluid findings and exclusion of alternative causes now help establish the diagnosis.^[ref]

Several mimics deserve explicit comparison. Mania can resemble the expansive mental phase, and depression or psychotic illness can resemble other presentations, but a sustained progressive combination of cognitive decline, characteristic speech disturbance and neurological signs argues for organic disease. Alcohol intoxication can produce tremor, slurred speech and an unsteady gait; an acute time course or improvement with clearance differs from progressive general paresis, although chronic alcohol-related disease may complicate the distinction. Other dementias, chronic cerebral vascular disease, tumours and some toxic or metabolic disorders can likewise combine cognitive and motor abnormalities.

A focal stroke generally gives a more abrupt and lateralised deficit; a series of strokes can produce a stepwise course. Parkinsonism can impair speech and gait but has a different predominant motor pattern. Tabes dorsalis can produce marked sensory ataxia, absent tendon reflexes and bladder disturbance with relatively preserved intellect; it can also coexist with paretic disease. The diagnosis rests on the pattern, course and corroborating investigation, not on grandiosity or a tremulous tongue alone.^[ref]

The brain needs continuous, locally matched perfusion within a nearly rigid skull. Its arterial connections, venous drainage, fluid compartments and vascular regulation meet different parts of that requirement. No single arrangement guarantees an unchanging intracranial blood volume or an uninterrupted supply under every condition.

There are two principal arterial approaches: the paired internal carotid arteries and the vertebral arteries, the latter joining as the basilar artery. At the base of the brain, the cerebral arterial circle connects the anterior and posterior supplies through communicating arteries. Connections between superficial cerebral arterial territories provide additional collateral routes. This permits redistribution if one route becomes inadequate, but individual anatomy varies, and some deep penetrating arteries have limited effective collateral supply. The existence of an anatomical circle therefore does not establish that any one artery can be obstructed harmlessly.^[ref]

The bends of the entering arteries and their branching course accompany a distributed vascular resistance and compliance. They should not be described as mechanically abolishing every pulse: cerebral blood flow remains pulsatile. Numerous small branches spread the supply over the surface before penetrating the tissue, while dense capillary networks bring exchange close to neurons and supporting cells.

Superficial and deep cerebral veins drain into dural venous sinuses. These are channels supported by folds and attachments of dura mater, rather than freely collapsible thin-walled veins. Their connections lead chiefly towards the internal jugular veins, with communicating vertebral, diploic and emissary routes providing additional possibilities. The valveless nature of many of these communications allows pressure-dependent changes of direction; it is not an assurance of one-way flow. Head position, neck pressure and the available alternative routes consequently matter to drainage.

The brain, blood and cerebrospinal fluid share the cranial enclosure. A small increase in one component can initially be accommodated by displacement of venous blood and cerebrospinal fluid, including fluid movement towards the spinal compartment. This reserve is finite. When compensation is exhausted, further volume increase can produce a large rise of intracranial pressure and reduce cerebral perfusion pressure. The skull does not make cerebral anaemia physically impossible, as an overly literal historical constant-volume argument might suggest.

A simplified pressure relation, useful in the modern account, iswhere CPP is cerebral perfusion pressure, MAP is mean arterial pressure and ICP is intracranial pressure. The approximation assumes that the effective downstream pressure is represented adequately by ICP; high venous pressure can complicate it. Cerebral autoregulation adjusts arteriolar tone and hence resistance when perfusion pressure changes. It has limited capacity and depends on physiological state, so a fixed universal pressure interval should not be inferred.^[ref]

Local metabolic regulation and neurovascular coupling also match supply to activity. A rise of arterial carbon dioxide tends to dilate cerebral vessels; vigorous overbreathing can lower arterial carbon dioxide and reduce cerebral blood flow. This is distinct from pressure-driven autoregulation. The blood-brain barrier, based principally on specialized capillary endothelium with tight junctions, helps stabilize the chemical environment while permitting regulated exchanges. It is a selective exchange arrangement, not the structure that supports the dural sinuses or generates the arterial pressure. These modern mechanisms refine the anatomical account without attributing all their molecular details to 1865.

The fourth ventricle is the cavity of the hindbrain between the dorsal surfaces of the pons and upper medulla oblongata anteriorly and the cerebellum posteriorly. It is continuous above with the cerebral aqueduct and below, at the obex, with the central canal of the spinal cord. Its floor is diamond-shaped when viewed from behind, while its roof rises dorsally towards the fastigium.

The floor, the rhomboid fossa, consists of an upper pontine triangle and a lower medullary triangle. Its upper apex points towards the cerebral aqueduct; its lower apex is the obex; the two lateral angles continue into the lateral recesses of the fourth ventricle. A median groove divides it into right and left halves. On each side, the medial eminence lies medial to the sulcus limitans, which separates predominantly motor territories medially from sensory territories laterally. The striae medullares of the fourth ventricle cross the floor near the junction of its pontine and medullary portions; their extent varies.

Several surface features identify deeper relations. In the pontine part, the facial colliculus overlies the abducens nucleus and the internal looping course of fibres of the facial nerve; it is not the exposed facial motor nucleus. The upper part of the sulcus limitans has the superior fovea, and near its rostral lateral region lies the locus coeruleus. Laterally, the vestibular area overlies the vestibular nuclei. In the lower triangle, the hypoglossal trigone overlies the hypoglossal nucleus, and the vagal trigone, lateral to it, overlies the dorsal motor nucleus of the vagus. The area postrema lies still farther caudolaterally, separated from the vagal trigone by the funiculus separans. These are landmarks and underlying relations, not claims that the cranial nerve nuclei lie loose within the cavity.^[ref]

The upper lateral boundaries are formed by the superior cerebellar peduncles. The lower lateral boundaries relate to the inferior cerebellar peduncles and adjacent dorsal medullary margins. The lateral recess on each side curves around the inferior cerebellar peduncle towards its external opening near the flocculus.

The roof has superior and inferior slopes. Superiorly the thin superior medullary velum spans the superior cerebellar peduncles, with the lingula of the cerebellum on its dorsal surface. Inferiorly, the roof relates to the inferior medullary velum, nodule of the cerebellum and thin tela choroidea. Vascular folds of the tela choroidea carry the choroid plexus of the fourth ventricle, with median and lateral extensions. The cavity has an ependymal lining; the choroid plexus has its specialized epithelial covering and produces cerebrospinal fluid.

There are three important exits to the subarachnoid space: one median aperture of the fourth ventricle through the inferior roof, opening towards the cisterna magna, and two lateral apertures of the fourth ventricle at the ends of the lateral recesses of the fourth ventricle. These must be distinguished from the inlet through the cerebral aqueduct and the inferior continuity with the central canal of the spinal cord. Most cerebrospinal fluid leaving the fourth ventricle reaches the subarachnoid space, not the narrow adult central canal of the spinal cord.

The three-dimensional arrangement explains the method of examination: reflecting the cerebellum and opening the delicate roof exposes the rhomboid fossa, but destroys part of the structure one is trying to describe. Studying an intact roof, then the exposed floor, and using a median section to locate the fastigium avoids interpreting a dissected cavity as naturally open behind. The modern nomenclature is useful here; not every fine landmark or physiological interpretation in this account should be read as an assertion about what an 1867 examiner required.^[ref]