ORBITAL MUSCLE ANATOMY
Here we have a coronal image of a T2 weighted orbital MRI! We see some of the frontal lobes and paranasal sinuses but we get a really good view of the muscles which form part of the ‘myofascial cone’
Identifying the muscle cone is useful when it comes to telling the difference between the different pathology that can affect the orbit
We can differentiate lesions as being predominantly either:
Extraconal (outside the muscle cone)
Infection is one of the most important causes - don’t miss a periosteal abscess! There commonly will be underlying paranasal sinusitis. Other causes include lymphoma, metastases (from breast and lung cancer) and sarcoid
Conal (originate within the muscle cone)
Most common culprits are pseudotumour and thyroid ophthalmopathy - the latter usually is bilateral and spares the tendinous insertion (known as the Coca Cola sign as the muscle looks like a bottle)
Intraconal (within the muscle cone)
Examples include cavernous haemangiomas (may see small foci of calcification), metastases and sarcoidosis
Intracanalicular (within the optic nerve)
Such as optic glioma or meningioma
Note on the annotations, LPS stands for levator palpebrae superioris - this muscle lifts the eyelid and is supplied by the oculomotor nerve