Thursday, November 29, 2012

80 - Tiger eye sign (Eye of the tiger sign)

- Lets begin from the basics and go on to the main stuff ....

*At birth, the central nervous system does not contain any iron in it.

*As the child grows into an adult there is (physiologically normal) gradual deposition of iron in the central nervous system.

*The part of the central nervous system where this iron deposition is most significant is the globus pallidus.

*Given below is an axial MRI image (T1 weighted) of the brain showing the exact location of the globus pallidus.

*Now this excessive iron deposition in the globus pallidus bilaterally with a central area of gliosis and edema changes gives the appearance of tigers eyes because of the different shape of globus pallidus.

*The peripheral iron appears hypointense (black on MRI) and the central gliosis and edema changes appear hyperintense (white on MRI) giving the appearance described above.

*One of the conditions in which this occurs is Hallervorden-Spatz syndrome.

*The exact image of the tiger eye sign cannot be posted here due to copyright issues, but you can see the image here ----> click here 

Saturday, November 3, 2012

79 - Meyer-Weigert law/rule

Due to embryological maldevelopment an entity called duplex collecting system develops in few people.

This looks like two kidneys on one side with the upper pole of the lower kidney attached to the lower pole of the upper kidney.

This law states that in cases like these the ureters have a typical drainage pattern into the urinary bladder where the ureter of the upper kidney or collecting system drains inferior and medial to the opening of the lower kidney or collecting system.

Typically this condition is also associated with development of ureterocele of the ectopic inserted ureter causing obstruction and reflux.

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