FIFTH CRANIAL NERVE LESIONS “The Birth of Venus”, (Detail), Tempera on canvas, Sandro Botticelli, c. 1485. Galleria degli Uffizi, Florence. “I think your whole life shows in your face, and you should be proud of that” Lauren Bacall A most beautiful inner serenity, almost haunting, still shows in the face of Sandro Botticelli’s Venus, even though painted well over half a millennium ago. Ms Bacall once mused, an individual’s whole history is reflected in their face. And so the face says much about the innermost and deepest sensations of the soul. Disharmonies of the sensations of the face may also reflect an inner disharmony of the Fifth Cranial Nerve! FIFTH CRANIAL NERVE LESIONS Introduction Cranial nerve V is also known as the Trigeminal nerve. It is the largest and most complex cranial nerve (although the vagus is the longest cranial nerve). It gives: ● Sensory innervation to the face, teeth, nasal cavity. ● Motor supply to the muscles of mastication. ● Motor supply to the additional muscles of tensor veli palatini and tensor tympani. The commonest lesions of the trigeminal nerve include herpes zoster infection, multiple sclerosis and trigeminal neuralgias. Other lesions of the trigeminal nerve are relatively uncommon. Variable facial numbness can be seen with presentations of MS. Anatomy Course of the Trigeminal nerve: The trigeminal nerve has its somatic efferent motor origins within the trigeminal motor nucleus within the pons. The trigeminal sensory nucleus contains the sensory relay nuclei for the trigeminal nerve. This is concentrated within the pons, however it extends extensively throughout the brainstem. The nerve emerges from the ventral aspect of the pons, via two roots, a large sensory root and a smaller motor root, to enter the middle cranial fossa. Near the apex of the petrous temporal bone the sensory root enlarges to form the trigeminal (or Gasserian) ganglion. From this ganglion arise the three major branches of the trigeminal nerve, the ophthalmic, the maxillary and the mandibular branches. The ophthalmic nerve is a purely sensory nerve and runs forward in the lateral wall of the cavernous sinus (below the 3rd and 4th cranial nerves). It emerges from the sinus to divide into 3 terminal branches, the lacrimal, frontal and nasociliary nerves, which all enter the orbit via the superior orbital fissure. The maxillary nerve is purely sensory and runs forward in the lower part of the lateral wall of the cavernous sinus to leave the skull through the foramen rotundum to enter the pterygopalatine fossa. The mandibular nerve is a motor and sensory nerve. Both the motor and sensory roots of the mandibular nerve leave the skull through the foramen ovale, and just after this the two branches unite. Trigeminal nerve innervations: The sensory innervations of the three divisions of the Trigeminal Nerve. 1 The 3 major branches of the Trigeminal Nerve are: 1. Ophthalmic: This divides into the following branches: ● Lacrimal nerve: ♥ Joined by parasympathetic nerve fibre branches from the Zygomaticotemporal, which later leave the nerve again. ♥ Sensory fibres to the upper lateral eyelid. ● Nasociliary nerve: ♥ Communicating branch (sensory) to the ciliary ganglion. ♥ Long ciliary nerve. ♥ Posterior ethmoidal nerve. ♥ Infratrochlear nerve. ♥ Anterior ethmoidal nerve (which becomes the external nasal nerve). ● Frontal nerve: ♥ Supratrochlear nerve. ♥ Supraorbital nerve. 2. Maxillary: Branches within the middle cranial fossa: ● Meningeal branches within the middle cranial fossa. Branches within the pterygopalatine fossa: ● 2 branches to the pterygopalatine ganglion. ● Posterior superior alveolar nerve. ● Zygomatic nerve. This further divides into: ♥ Zygomaticotemporal nerve (also gives off post-ganglionic parasympathetic nerve fibres to the lacrimal nerve). ♥ Zygomaticofacial nerve. Branches within the orbit: ● Middle superior alveolar nerve. ● Anterior superior alveolar nerve. ● Infraorbital nerve. 3. Mandibular: Branches from the main trunk of the mandibular nerve: ● Meningeal branches. ● Nerve to the medial pterygoid - innervates the medial pterygoid muscle, and via two branches of this nerve, passing through the otic ganglion to supply the “two tensors” - the tensor veli palatini muscle and the tensor tympani muscle. Branches from the anterior division of the mandibular nerve, (3 motor nerves and one sensory nerve): ● Nerve to masseter. ● Nerve to temporalis. ● Nerve to the lateral pterygoid. ● Buccal nerve (sensory). Branches from the posterior division of the mandibular nerve: ● Auriculotemporal nerve: ♥ This is a sensory nerve that supplies the auricle, the outer tympanic membrane and the temporal region of the face and head. ♥ It also supplies the temporomandibular joint. The otic ganglion gives parasympathetic branches (from the glossopharyngeal nerve) to the auriculotemporal nerve, which then carries these parasympathetic nerve fibres to the parotid gland. The otic ganglion therefore is actually functionally separate from the mandibular nerve. It is functionally part of the glossopharyngeal nerve, conveying parasympathetic fibres from the glossopharyngeal nerve to the parotid gland, via the otic ganglion. ● Lingual nerve: ♥ This is joined by the chorda tympani branch of the facial nerve, which carries the special sense of taste. ♥ The lingual nerve itself conveys general sensation to the anterior two thirds of the tongue, as well as the floor of the mouth. ♥ The submandibular ganglion is also attached to the lingual nerve. This ganglion conveys parasympathetic nerve fibres from the facial nerve, which pass through the submandibular ganglion, to go on to supply the submandibular gland. So while the submandibular ganglion is anatomically part of the lingual nerve, it is actually functionally part of the facial nerve. ● Inferior alveolar nerve: ♥ Gives off the nerve to the mylohyoid, (which also supplies the anterior belly of the digastric muscle). ♥ Gives sensory supply to the teeth of the lower jaw. ♥ Terminates as the mental nerve, which gives sensory supply to the skin around the chin. Pathology Causes of lesions of the trigeminal nerve include: Central lesions: Lesions of the pons, medulla and upper cervical cord may occur as result of: ● Vascular lesions. ● Tumour. ● Demyelination (MS). ● Syringobulbia. Peripheral lesions: 1. Space occupying lesions within the middle cranial fossa: ● Tumour (meningiomas, acoustic neuromas). ● Aneurysm. 2. Cavernous sinus lesions (thrombosis, tumours, aneurysms) : These may affect: ● The maxillary and mandibular divisions of the trigeminal nerve. ● Cranial nerve III. ● Cranial nerve IV. ● Cranial nerve VI. 3. Trauma: ● Fractures of the base of the skull within the region of the middle cranial fossa. 4. Mononeuritis conditions (rare): Causes of these may include: ● Connective tissue diseases, (microvascular lesions). ● Diabetes mellitus. ● Alcohol. ● Paraneoplastic phenomena. ● Sarcoidosis. ● HIV. Clinical Assessment The trigeminal nerve is tested as follows: 1. Corneal reflex: Gently brush the cornea (not the conjunctiva) with a cotton bud bought to the eye from the side. A normal corneal reflex results in the blinking of both eyes. The patient should be asked if the touch of the cotton wool has been felt. The afferent sensory pathway of the reflex is conveyed by the ophthalmic branch of the trigeminal nerve. The motor blinking response is conveyed by the facial nerve via its innervation of the orbicularis oculi muscles. If blinking only occurs in the contralateral eye, this will indicate an ipsilateral facial nerve palsy. The patient will still perceive the touch of the cotton wool on the cornea. If neither eye blinks in response, and the cotton wool is not perceived, then there is a lesion of the ophthalmic nerve. 2. Facial sensation: Each division of the trigeminal nerve should be tested for sensory deficit. Each side should be compared with the other. Pain sensation is tested with a sterile needle, (or sharpened wooden spatula - less likely to draw blood!), while the patient has their eyes closed. Loss of pain sensation results only in a dull sensation, rather than a sharp one. Testing is best done from dull to sharp areas. Temperature is not routinely tested as its loss is usually accompanied by loss of pain sensation. It is tested for if syringobulbia is suspected. Proprioception is not routinely tested (and would be somewhat problematic!). Light touch is then tested using a cotton wool bud, again comparing both sides. The skin should be touched rather than stroked. The patient should be tested with their eyes closed and indicate a positive result by saying “yes”. 3. Motor function: Look for wasting of the temporal or masseter muscles. Ask the patient to clench their teeth, and feel for the muscle bulk of the masseters. Ask the patient to open the mouth and to hold it open against the examiner's resistance. This tests the pterygoid muscles. A unilateral lesion of the motor division will cause the jaw to deviate towards the weak (i.e. affected) side. 4. Jaw jerk reflex: The patient lets the jaw hang open. The examiner's finger is placed in the symphysis menti of the jaw. The examiner then gently taps his/her finger with the tendon hammer. A normal reaction is a slight closure of the mouth, or no response at all. In upper motor neuron lesions (above the pons), the jaw jerk will be greatly enhanced, and this response in commonly seen in cases of pseudobulbar palsy. Loss of sensation in all 3 of the major divisions of the trigeminal nerve implies a lesion that is either central,