Townes view

It is taken with the patient in the supine position and lying on his back with the chin often depressed into the neck. 

The X-ray camera is angled at 30 degrees towards the feet so that the rays enter the head at the level of the hair-line.

The result is clear image of the posterior portion of the skull including the foramen magnum.

A reversed Towne's view is obtained by taking the radiograph from the posterior with the patient lying face down.

The stuctures that are demonstrated in Town's view are

Details of occipital bone(1)

Lambdoid suture (2)

Outline of Foramen magnum (3)

Dorsum Sellae (4) (White shadow in the foramen magnum)

Occipital crest (5)

Some of the details of the temporal bone like petrous ridge are also identified (1)

Angiographic Shifts Seen With IC Masses

When cerebral angiography was the mainstay of diagnosis certain displacements of the vessels principally pericallosal vessels in the angiogram were used as indirect evidences for the location of the masses in various regions of the brain.

These shifts are

• Round shift = Frontal lesion anterior to coronal suture
• Square shift = Lesion behind foramen of Monro in lower half of hemisphere
• Distal shift = Posterior to coronal suture in upper half of hemisphere
• Proximal shift = Basifrontal lesion / anterior middle cranial fossa including anterior temporal lobe

Sylvian Point (Angiographic)

The angiographic sylvian point (ASP) is the most medial point where the last cortical MCA branch ( usually the angular artery) turns inferiorly to exit the sylvian fissure. 

This point approximates the apex of the insula and represents the posterior limit of the lateral cerebral sulcus. 

It is suggested to be the halfway point on the clinoparietal line (CPL) (CPL is the line between the anterior clinoid process and a pointon the skull roof situated 2 cm above the lambda or 8to9 cm obove the external occipital protrubarence).

It is seen in tha AP view.

Sylvian triangle (Angiographic)

Sylvian triangle =  A triangle formed by branches of MCA within sylvian fissure on outer surface of insula (form a loop) upon reaching the upper margin of the insula.

Anatomically it is demarcated by the superior insular line ( A line tangent to the tops of the insular loops), The main MCA trunk ( forms the posterior inferior margin of the triangle) and the most anterior branch of the ascending frontal complex ( forms the anterior border of the triangle) 

It is seen in lateral view and serves as angiographic landmark for localizing supratentorial masses. 

Schlesinger in 1953 identified and publicized this.

Radiation Necrosis

Necrosis of brain following radiation can be seen as an early delayed complication or late delayed complication.
The early delayed radiation necrosis may be seen with in 2 months of irradiation (Range 1 to 4 Months). This is a very rare entity. The pathological process might represent an autoimmune response following sensitization by a necrobiotic process induced by radiation.

The late delayed radiation necrosis commonly presents as a mass lesion.
The true incidence and natural history of late delayed radiation necrosis are not known. Most commonly late delayed radiation affects present at a mean duration of 14 months, but can occur as early as 6 months or as late as 5 years after completion of treatment.
The primary mechanism of the late delayed radiation necrosis is coagulative necrosis affecting the white matter secondary to small artery endothelial injury or direct damage to oligodendroglia.
Its incidence has been estimated as 5% in patients who have received greater than 45 Gy in fractions of 2 Gy per day.
25% of patients may suffer from radiation necrosis if the areas of the brain have received a total radiation dose of 60Gy or more.
4 facors critical in the occurance of radiation necrosis are
1. Total dose of radiation
2. Overall time of administration
3. Size of each fraction of Radiation
4. Number of fractions per irradiation