Posterior Fossa Lesions

Appendicitis Diagnosis By CT

Diagram displaying appendicitis clinical course and complications.

Appendicitis is inflammation of the vermiform appendix caused by an obstruction attributable to infection, stricture, fecal mass, foreign body or tumor. Appendicitis can affect either gender at any age, but is most common in males ages 10 to 30. Appendicitis is the most common disease requiring surgery. If left untreated, appendicitis may progress to abscess, perforation,peritonitis, and death.

Gallbladder Ultrasound Evaluation

                       Micky Mouse 

Carotid Sinus Hypersensitivity

In people with carotid sinus hypersensitivity (exceptional responsiveness of the carotid sinuses in various types of vascular disease), external pressure on the carotid artery may cause slowing of the heart rate, a fall in blood pressure, and cardiac ischemia resulting in fainting (syncope). In all forms of syncope, symptoms result from a sudden and critical decrease in cerebral perfusion.

Diagram displaying the right way to measure the arterial pulse.

Consequently, this method of checking the pulse is not recommended for people with cardiac or vascular disease. Alternate sites, such as the radial artery at the wrist, should be used to check pulse rate in people with carotid sinus hypersensitivity.

Carotid Bodies

The carotid bodies are in an ideal position to monitor the oxygen content of the blood before it reaches the brain. Decrease in PO₂ (partial pressure of oxygen), as occurs at high altitudes or in pulmonary disease, activates the aortic and carotid chemoreceptors, increasing alveolar ventilation. The carotid bodies also respond to increased carbon dioxide (CO₂) tension or free hydrogen ions in the blood.

Diagram displaying right carotid artery and the position of the carotid body and its innervation.

The glossopharyngeal nerve (CN IX, perhaps with involvement of the vagus nerve) conducts the information centrally, resulting in reflexive stimulation of the respiratory centers of the brain that increase the depth and rate of breathing. The pulse rate and blood pressure also increase. With the increased ventilation and circulation, more oxygen is taken in and the concentration of CO₂ is reduced accordingly.

Brain Ventricular System

The ventricular system of the brain consists of two lateral ventricles and the midline 3rd and 4th ventricles connected by the cerebral aqueduct. CSF, largely secreted by the choroid plexuses of the ventricles, fills these brain cavities and the subarachnoid space of the brain and spinal cord.

The ventricular system and circulation of the CSF are shown. The production of CSF is mainly by the choroid plexuses of the lateral, 3rd, and 4th ventricles. The plexuses of the lateral ventricles are the largest and most important. CSF is absorbed into the venous system through the arachnoid granulations that project into the superior sagittal sinus and its lateral lacunae.

The subarachnoid cisterns, expanded regions of the subarachnoid space, contain more substantial amounts of CSF.

The lateral ventricles, the 1st and 2nd ventricles, are the largest cavities of the ventricular system and occupy large areas of the cerebral hemispheres. Each lateral ventricle opens through an inter-ventricular foramen (foramen of Monro) into the 3rd ventricle. The 3rd ventricle, a slit-like cavity between the right and the left halves of the diencephalon, is continuous postero-inferiorly with the cerebral aqueduct, a narrow channel in the midbrain connecting the 3rd and 4th ventricles. The pyramid-shaped 4th ventricle in the posterior part of the pons and medulla extends infero-posteriorly. Inferiorly, it tapers to a narrow channel that continues into the cervical region of the spinal cord as the central canal. CSF drains into the subarachnoid space from the 4th ventricle through a single median aperture (Foramen of Magendie) and paired lateral apertures (foramina of Luschka). These apertures are the only means by which CSF enters the subarachnoid space. If they are blocked, CSF accumulates and the ventricles distend, producing compression of the substance of the cerebral hemispheres.