Brain fossae

The pituitary gland is situated in sella turcica or hypophyseal fossa of the sphenoid bone attached to the brain by a stalk which is continuous with the part of brain i.e. hypothalamus and there is a communication between the hypothalamus and the pituitary gland by means of nerve fibres and a complex of blood vessels. Pituitary gland consists of three parts - anterior lobe or adenohypophysis, posterior lobe or neurohypophysis and middle lobe or pars intermedia. 

A 19-year-old woman became disoriented and had hyponatremia (131 mmol/1) and a serum ethanol concentration of 2.4 mmol/1. Her serum sodium had fallen to 120 mmol/1 10 hours later, and 5 hours later she suddenly deteriorated and had a respiratory arrest, coma, and sinus tachycardia of 180/minute with bige-miny. A CT scan showed diffuse edema in the posterior fossa. She was considered brain dead 23 hours after taking the ecstasy. 

The hematoma continues to expand after stroke onset, frequently causing further deterioration (Brott et al. 1997 Leira et al. 2004). Some brainstem hemorrhages evolve subacutely, particularly those caused by a vascular malformation (O Laoire et al. 1982 Howard 1986). Any large hematoma may cause brain shift, transtentorial herniation, brainstem compression and raised intracranial pressure. Hematomas in the posterior fossa are particularly likely to cause obstructive hydrocephalus. Rupture into the ventricles or on to the surface of the brain is common, causing blood to appear in the subarachnoid space. 

Different neoplasms of brain predominate in adults and in children. More pediatric neoplasms occur in the posterior fossa than in the anterior fossa, and the opposite is true of adult neoplasms. 

T2- and FLAIR-weighted sequences typically demonstrate bilateral, symmetric hyperintensity, and swelling in subcortical white matter and overlying cortex in the occipital, parietal, and posterior temporal lobes as well as the posterior fossa. The posterior circulation predominance is thought to result from the fact that there is less sympathetic innervation (which supplies vasoconstrictive protection to the brain in the setting of acute hypertension) in the posterior compared with the anterior circulation. However, anterior circulation lesions are not uncommon and are frequently in a border-zone distribution. 

The brain resides within the cranial cavity. The bony roof and sides of the cranial vault make up the calvaria, which is composed of frontal, temporal and parietal bones and a small portion of the occipital bone. The floor of the cranial vault is divided into three depressions or fossae the anterior fossa extends from the region superior to the orbits and nasal cavity caudaUy as far as the posterior margin of the lesser wing of the sphenoid the middle fossa occupies the region between the lesser wing of the sphenoid and the anterior border of the petrous portion of the temporal bone and the posterior fossa, is underlain by the remainder of the temporal bones and the occipital bone. 

Caudal to the thalamus are the midUne structures of the brainstem the midbrain, pons, and medulla oblongata. Dorsal to the pons, but inferior to the tentorium cere-belli, is the cerebellum which is the prominent structure in the inferior cranial fossa. The brainstem as a whole is concerned with somatosensory information from the neck and head as well as the specialized senses of taste, audition and balance. It acts as a conduit for ascending and descending pathways of motor and sensory information between the cortical regions of the brain and the body. In addition, the brainstem is responsible for mediating levels of consciousness and arousal. 

In cases of basilar impression, CT of the cranium and upper cervical spine can image the invaginated odontoid process and other bony anomalies. A typical CT finding is a complete dense ring of bone on the lower cut of the posterior fossa at which level in normal cases there is still brain tissue (Boles et al. 1977). Moreover, such accompanying anomalies as syrinx, Chiari malformation, hydrocephalus are also detectable (di Chiro and Schellinger 1976, Nakagawa et al. 1977, Lee et al. 1978, Oberson and Azam 1978, Carella et al. 1981, Isu et al. 1983). 

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