Sixth Nerve (Abducens Nerve) Palsy

The abducens nerve  (Cranial Nerve VI) innervates the lateral rectus muscle and is the most common single muscle palsy, causing loss of abduction and resultant horizontal diplopia, worse in ipsilateral
gaze. Associated findings are dependent on the location of the lesion.

Etiology: Within the pons, involvement of the corticospinal tract results in contralateral hemiparesis. The abducens has the longest intracranial course of any nerve, and therefore is vulnerable to stretching or compression secondary to elevated intracranial pressure, trauma, neurosurgical manipulation, and cervical traction.

 Also, any meningeal process (infectious, inflammatory, or neoplastic) can affect this portion of the sixth nerve.

Aneurysmal compression is uncommon.

Prior to entering the cavernous sinus, the nerve crosses the petrous portion of the temporal bone. Trauma with temporal bone fracture can result in a combination of sixth- and seventh-nerve palsies.

Cavernous sinus pathology is suggested by the involvement of the internal carotid artery, venous drainage of the eye and orbit, trochlear and oculomotor nerves, the first division of the trigeminal nerve, and the ocular sympathetics.

Microvascular changes secondary to diabetes, hypertension, and giant cell arteritis can compromise
function.

                  Sixth-Nerve Palsy. Loss of abduction of the left eye is seen in lateral gaze.

Management:
Associated signs and symptoms guide the workup.

Horner Syndrome - Clinical Features And Management

Horner syndrome (miosis, ptosis, and anhidrosis) is secondary to loss of ocular sympathetic innervation.

• Ptosis is less than 2 mm, the result of paralysis of Müller muscle, innervated by the sympathetic pathway. 
• Anhidrosis is often not apparent to patients or clinicians. 
• A pupillary finding specific in Horner syndrome is dilation lag. Because the dilator muscle is weak,
• the pupil dilates more slowly than the normal pupil.

This loss of ocular sympathetic innervation can be produced by a lesion anywhere along a three-neuron sympathetic pathway, from the hypothalamus down through the brain stem to the cervical cord, in the apex of the chest, along the carotid sheath, and in the cavernous sinus or orbit.
Isolated Horner syndrome presenting with head or neck pain suggests an internal carotid artery dissection.

Management
Associated signs and symptoms help direct the workup. A patient with cranial nerve abnormalities requires CT or MRI imaging and admission. In the setting of cervical spine trauma, neck immobilization and appropriate imaging studies are instituted. Consider carotid artery dissection in neck pain without trauma.

Uncal Herniation Syndrome After Severe Head Injuries

Severe head injury can result in extra-axial hematoma, cerebral contusion, or diffuse cerebral edema which, in turn, may cause one of five brain herniation syndromes:

1. uncal, 
2. central
3. transtentorial, 
4. cerebellotonsillar, 
5. subfalcine, and external.

Uncal herniation occurs when the uncus of the temporal lobe is displaced inferiorly through the medial edge of the tentorium.
Compression of cranial nerve III can cause an ipsilateral dilated pupil. Typically, patients with uncal herniation are unconscious and require intubation. A contusion to the eye may also result in a dilated, non responsive pupil and arouse suspicion for severe head injury and uncal herniation
but typically these patients will be alert.

                                         Ipsilateral Dilated Pupil due to Uncal Herniation.
      ( CT revealed an epidural hematoma and unilateral effacement of the quadrigeminal cistern. )

Management: Intubate unconscious head trauma patients with a unilateral dilated pupil and transfer them immediately to a facility capable of caring for traumatic brain injury. A noncontrasted head CT scan can identify a subdural or epidural hematoma, diffuse edema, or temporal lobe contusion. These conditions often cause midline shift of cerebral structures and compression of the quadrigeminal cistern. Unilateral effacement of the quadrigeminal cistern confirms uncal herniation.

Different Types Of Tremors - Chart

Depressed Skull Fracture

Depressed skull fractures typically occur when a large force is applied over a small area. They are classified as open if the skin above them is lacerated. Abrasions, contusions, and hematomas may also be present over the fracture site.
The patient’s mental status is dependent upon the degree of underlying brain injury. Direct trauma can cause abrasions, contusions, hematomas, and lacerations without an underlying depressed skull fracture.  Evidence of other injuries such as a basilar fracture, facial fractures, or cervical spinal injuries may also be present.

                                            CT demonstrating depressed skull fracture. 

Management: Explore all scalp lacerations to exclude a depressed fracture. CT should be performed in all suspected depressed skull fractures to determine the extent of underlying brain injury.

• Depressed skull fractures require immediate neurosurgical consultation. 
• Treat open fractures with antibiotics and tetanus prophylaxis as indicated. 
• The decision to observe or operate immediately is made by the neurosurgeon. 

Differential Diagnosis Of Normal Pressure Hydrocephalus (NPH)

       Noncontrast CT demonstrates enlarged lateral ventricles without significant cerebral atrophy

Normal Pressure Hydrocephalus (NPH) can be idiopathic or secondary to meningitis, subarachnoid hemorrhage, or head trauma, and is caused by impaired reabsorption of spinal fluid. Patients present with gait abnormalities, urinary
incontinence, and/or cognitive impairment. Diagnosis is confirmed by radiographic evidence and a normal opening pressure on lumbar puncture.

Differential Diagnosis:
• Alzheimer disease—Impaired orientation and memory, which are often spared in NPH; cortical atrophy.

A Case Of Normal-pressure hydrocephalus

A 75-year-old man is brought in to your office by his wife. She complains that he is not the same over the last 6 months. His memory is failing him, he has difficulty walking (especially when he initiates walking), and he is incontinent of urine. Which of the following is the most likely diagnosis based on his history?

Answer: Normal-pressure hydrocephalus (NPH)

Discussion:  Normal-pressure hydrocephalus(NPH) is a cause of dementia in the elderly. It may be
caused by previous insult to the brain, usually as a result of a subarachnoid hemorrhage or diffuse meningitis that presumably results in scarring of the arachnoid villi over the brain convexities where cerebrospinal fluid (CSF) absorption usually occurs. However, elderly NPH patients seldom have a
history of predisposing disease.

NPH classically consists of

• dementia,
• apraxia of gait, and 
• incontinence 

A Child Brought For Evaluation Of Seizure Disorder- A Distinct Birth Mark Seen On Face

This female child was brought to the pediatrician for the evaluation of seizure disorder. On examination , a vascular plaque was found along the ophthalmic and maxillary divisions of the trigeminal nerve. (as shown in picture ) . Mother is not concerned about the lesion mentioning it has been present since birth and since then there has been no change in morphology, neither it has caused any pain to the child, other than the cosmetic defect.

The most likely possibility is:

A. Infantile hemangioma
B. Struge Weber syndrome.
C. Congenital Hemangioma
D. Proteus syndrome.

Answer An d Discussion:

Acute Subdural Hematoma

A 34-year-old driver was hit from behind at approximately 25 mph. He hit his head, but did not lose consciousness and did not seek care. Approximately 12 hours later, he developed a headache and confusion, and was taken to the emergency department by a family member. He was found to have an acute subdural hematoma . (Picture shown below). He was hospitalized, and a neurosurgeon was consulted for surgical management.

CT scan of an acute subdural hematoma (arrow) seen as a hyperdense clot with an irregular border. There is a midline shift from the mass effect of the accumulated blood.

Case Discussion

Subdural hematomas (SHs) can occur at any age, but are most common in infants and older adults. Most SHs are caused by trauma.