In many cases of crossed paralysis, besides common motor and sensory symptoms, there is apt to be neuro-retinitis with its consequences.
The chief forms or types of crossed paralysis are:
(α) Lesions involving the meso-ventral aspect of one crus cerebri. The direct symptoms of such a lesion are in the range of distribution of the motor oculi (N. iii.), such as ptosis, mydriasis, external strabismus, and heteronymous diplopia; the crossed symptoms are more or less complete paralysis of the lower part of the face and of the extremities on the opposite side (hemiplegia). This relatively frequent form of crossed paralysis we designate as the eye-and-body type.
(β) The lesion occupies the latero-ventral part of the crus. This rare localization would give rise to direct paralysis of the fourth nerve, indicated by homonymous diplopia in the lower inner field of vision; to lateral hemianopsia with dark half-fields opposite the lesion, from injury to the tractus opticus (vide [Fig. 8]); and to a mixed motor and sensory disturbance in the opposite side of the face and body, without anæsthesia of the olfactory and auditory apparatus. A very large lesion involving almost the entire crus would probably also cause direct paralysis of N. iii.
(γ) Lesion of the basal part of the pons frontad of an imaginary transverse line passing through the apparent origin of the trigemini (NN. v.). Symptoms: A common hemiplegia of the lower face and extremities on the opposite side with neuro-retinitis and other general signs of basal disease. The abducens nerve (N. vi.) would in some cases be involved in its course frontad over the pons, giving rise to internal strabismus and homonymous diplopia on the same side as the lesion.
(δ) A focal lesion in the caudo-ventral part of the pons—i.e. caudad of an imaginary transverse line passing through the trigeminus roots—gives rise to highly characteristic symptoms. These are: Direct paralysis of the face, not (?) affecting all the muscles, but without De R., and common hemiplegia of the limbs on the opposite side.
If the lesion be strictly basal—i.e. one springing from the membranes or bone, the trunks of the sixth and seventh (facial) nerves are directly injured, and the resulting facial paralysis is of the peripheral form, affecting all the muscles and yielding De R. The body symptoms on the side opposite the lesion are less marked.
In the first category of cases, those in which the lesion is in the substance of the pons, the motor fasciculus from the cortex cerebri to the nucleus of N. vii. is injured caudad of (below) its theoretical decussation-point on the middle part of the pons, while the pyramidal tract is involved frontad of (above) its decussation.
This symptom-group is known as face-and-body type, or as crossed hemiplegia, strictly speaking.