PATH:

• It exits the posterior cranial fossa through the Hypoglossal Canal, which is anterior to the Occipital Condyles.
• It may pass through the Carotid Sheath or on either side of it.
• It passes toward the tongue medial to the posterior belly of the Digastric muscle.
• Upper portions of the Ansa Cervicales will hang off the Hypoglossal in order to reach the strap muscles, but the fibers do not intermix.

DAMAGE TO HYPOGLOSSAL:

1. It would be difficult to stick tongue out.
2. The tongue would deviate toward the nonfunctional side, due to functional muscles protruding it in that direction.

• If tongue deviates to the left, then damage is to the left hypoglossal nerve.

Aneurysms: are localized abnormal dilations of vessels; most common and significant are abdominal aortic aneurysms.

Causes: any that results in damage or weakness of vessel walls

• Atherosclerosis and cystic medial degeneration (two most common)

• Syphilis

• Vasculitis (e.g. polyarteritis nodosa - PAN)

• Hypertension: role in dissecting aneurysms

• Trauma (e.g. false aneurysms, arterio-venous aneurysms)

• Congenital defects: familial predisposition to other causes

• Infections (mycotic aneurysms): from septic embolisms or direct septicaemia

Abdominal Aortic Aneurysms: are typically found in men >50 years old.

The risk of rupture increases with the maximal diameter of the bulge: minimal risk if <5cm>5cm; operative mortality is 5% for unruptured aneurysm but >50% after rupture.

Because atherosclerotic peripheral (aortic) vascular disease is usually accompanied by severe coronary atherosclerosis, patients with abdominal aortic aneurysms have a high incidence of ischemic heart disease.

Complications: morbidity and mortality of (aortic abdominal) aneurysms are secondary to

• Rupture into peritoneal cavity or retroperitoneal tissues with massive fatal haemorrhage.

• Impingement on adjacent structures (e.g. compression of ureter or erosion of vertebrae)

• Occlusion of proximate vessels by either extrinsic pressure or superimposed thrombosis (e.g. renal, mesenteric arteries)

• Embolism from mural thrombosis

Sometimes there may be inflammation around the aneurysm in the adventitia, together with fibrous scarring. Rarely the aneurysm may become infected from a bacteraemia.