Injury to the facial nerve and its branches can cause paralysis to the facial muscles on the ipsilateral side. This condition is known as Bell's palsy. The patient will appear to have odd facial expression on one side, that is distorted because of a lack of muscle tone. This paralysis can have ramifications other than lack of muscle control. The loss of control of the orbicularis oris can cause the inferior eyelid to drop, and thus lacrimal fluid cannot inundate the cornea. These leads to a lack of proper hydration and lubrication of the cornea, which make it susceptible to laceration. Such an injury could lead to impaired or lost vision. The parotid gland is the largest of the three salivary glands. Like the other two glands, the parotid secretes saliva through ducts into the oral cavity to aid in mastication and swallowing. As previously mentioned, the facial nerve travels into the parotid gland where it becomes the parotid plexus of facial nerves and branches to the face. The parotid duct travels from the the parotid gland anteriorly, pierces the buccinator, and enters the oral cavity in order to secrete saliva into the mouth.
The parotid gland may become infected and inflammed by a bloodstream pathogen. Most commonly, this pathogen is the viral agent of mumps. The swelling that results from the inflammation can cause severe pain because the glands expansion is limited by the parotid sheath. The pain is often the worst during chewing because of the increased compression by the mandible and mastoid process. The mumps virus can also lead to inflammation of the parotid duct, which can often be confused with a toothache. Since the parotid gland shares common sensory fibers with the auricular and temporal regions, patients often experience referred pain in those ares from inflammation of the parotid gland.
The cerebral arterial circle or Circle of Willis, is an anastomosis located at the base of the brain that supply blood to the brain. The circle of vessels include: the anterior communicating artery, the anterior cerebral arteries, the internal carotid arteries, the posterior communicating arteries, and the posterior cerebral arteries. Anatomic variation in commonplace in the Circle of Willis. Variation in the size of the vessels is most common, but sometimes certain vessels are absent or duplicated. The resultant size of the vessels from these variations, whether larger or smaller, can become significant if problems in vascular integrity and/or blood flow occur.
In an ischemic stroke, blood flow the certain areas of the brain is decreased (likely due to an embolism), which can lead to deficits in the affected areas. This results in the patient presenting with sudden onset of neurological symptoms. The Circle of Willis can act as a secondary source of circulation if there is an obstruction of a major artery within the circle. By diverting some of its normal flow to the areas not receiving blood because of the obstruction, it can help maintain the function of those tissues. The circle sometimes cannot compensate for the blockage due to the anatomical variation or to the inadequacy of the vasculature in elderly. The other type of stroke that can occur in this anastomoses is a hemorrhagic stroke, cause by the rupture of an artery (known as an aneurysm). This can ultimately lead to large amounts of bleeding into the subarachnoid space, which requires urgent medical attention.
References
Moore et al. "Clinically Oriented Anatomy" (2010) 6th ed
Jonas: Mosby's Dictionary of Complementary and Alternative Medicine. (c) 2005, Elsevier.
http://meded.ucsd.edu/clinicalimg/head_parotitis.htm
http://health.allrefer.com/health/stroke-circle-of-willis.html
