Friday 7 October 2011

Orbital Pseudotumour MRI

A 50 yo male with right orbital proptosis, painful eye movement and conjunctival congestion.

MRI and CT (P+C) dated 19-Sept 11: 
This MRI study shows:
Right side,
Mild orbital proptosis.
A well circumscribed intra orbital focal lesion tear drop shape on axial sections , its narrower end towards orbital foramen.
Signals of lesion on MR and density on CT are unusual; on MR isointense to orbital fat on T1w and T2w with complete signal suppression on STIR. But on CT density does not follow fat, it is soft tissue density, isodense, isodense to adjacent muscle and show moderate homogenous enhancement on post contrast CT. Size ~ 16x8mm
Bony floor of right orbit intact.
No marked mucosal thickening in right maxillary antrum or adjacent ethmoid air cells.
Region of naso lacrimal duct normal.
Inferior and medial rectus normal. Mass is not arising from recti.
Plane of this tissue appears to be partly intraconal and partly extraconal; as on axial sections it appears to be within the muscle cone but on coronal sections mild elevation of medial end of adjacent inferior rectus.
No superior ophthalmic vein enlargement.
This soft tissue is not arising from optic nerve. Optic nerve is mildly displaced by this tissue.
No intra cranial extension.
No obvious bony orbital margin destruction.
Intra orbital fat show normal density on CT and signals on MR.

Follow up MRI dated 29 Sept 11: 
This MRI study shows marked regression in size of the lesion compared to previous MRI.

Conclusion :
Comparison of MR dated 19-Sept 11 with 29-Sept 11 show marked regression in size of the lesion in just 10 days.
Meanwhile pt was on steroids.
This narrows the list of differentials to Pseudotumour and Lymphoma - Both are known to respond to steroids. Short history of right orbital pain, painful eye movement and conjunctival congestion on clinical examination goes more in favor of Pseudotumour.

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