Midbrain – Transverse View  – Concepts

Ashley Davidoff MD

The Common Vein Copyright 2010

Introduction

On cross sectional imaging the midbrain is relatively short and has similar shape to other structures in the region.  In general it is almost butterfly shaped.

Two Rectangles

Two Ovals and a Tiny Sphere

The midbrain consists conceptually of twoanteroleaterally positioned rectancles, and two posterocentrally placed ovals (purple), surrounding the small aqueduct of Sylvius (white).

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Baseline Shape of the Midbrain

Sting Like a Butterfly

The midbrain is almost butterfly shaped with rounded posterior borders (colliculi) and rectangular shaped wings – the cerebral peduncles. It is very similar in shape to the pons and medulla on axial imaging but a a few characteristics distinguish it from these structures, most specific of which is the aqueduct of Sylvius that run right through its substance posteriorly shown as a black circle

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94074b09b01a08.8s

94074b09b01a08.8s The midbrain consists conceptually of two anteroleaterally positioned rectancles, and two posterocentrally placed ovals (purple), surrounding the small aqueduct of Sylvius (white).

Courtesy Ashley Davidoff MD copyright 2010 all rights reserved

The Midbrain within the Context of the Whole Brain  

T2 Weighted MRI

The T2 weighted MRI series focuses on the midbrain with characteristic shape and the small aqueduct of Sylvius posteriorly.  It is surrounded by portions of the frontal lobe anteriorly, temporal lobes laterally and perhaps small portions of the occipital lobes posteriorly.

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Cerebral Crura and Colliculi

Tectum and Tegmentum

The posterior end of the midbrain is bordered by the colliculi (purple) in the tectum (roof) of the nidbrain. The anterior border is bordered by the crura cerebri (green) in the cerebral peduncles and tegmentum (floor of the midbrain)

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Peduncles Substantia Nigra Tegmentum Colliculi and Tectum

The anterior border iof the midbrain incorporates the cerbral peduncles(green), and the substantia nigra (black – just posterior to the peduncles. Between the substantia nigra and the aqueduct is an area of the midbrain called the tegmentum (floor of the midbrain) The posterior end of the midbrain is bordered by the colliculi (purple) in the tectum (roof) of the nidbrain.

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The Cerebral Crura and the Colliculi

The Tegmentum and the Tectum

 The T2 weighted MRI series focuses on the midbrain with characteristic shape and the small aqueduct of Sylvius posteriorly. The cerebral crura are now shown anteriorly (green) in the cerebral peduncles, and the colliculi are shown posteriorly in the tectum or roof posteriorly

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The Cerebral arteries Characteristically Surround the Midbrain

The MRI T2 weighted series now focuses on another very characteristic feature of the midbrain in that it is surrounded by the anterior and posterior cerebral circulations, and in this case portions of the arteries are seen with parts of the middle cerebral seen anteriorly and parts of the posterior cerebral seen posteriorly

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The Face of a Baby Pig

As we start to delve into the complexity of the nuclii of the midbrain the shape takes the form of the head of a baby pig

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