Nontraumatic Orbital Hemorrhage (NTOH)

• Non-traumatic orbital hemorrhage (NTOH) occurs in several distinct patterns: – (1) subperiosteal hemorrhage (NTSOH), usually due to a sudden rise in cranial venous pressure, almost always in the superior orbit. – (2) hemorrhage related to extraocular muscles or their sheath, most commonly the inferior rectus. – (3) hemorrhage within the capsule surrounding alloplastic implants, usually in the orbital floor. – It can also occur diffusely within the orbital soft tissues, or secondary to vascular malformations. • Hemorrhage related to the inferior rectus or its sheath is seen as a well-defined orbital mass, with smooth enlargement of the belly of the IR muscle or its sheath or the intermuscular septum, in a tear-drop configuration, tapering towards the orbital apex. • Inferiorly located hemorrhages have been described as having the appearance of a beached whale. • Subperiosteal hemorrhages have a characteristic lenticular or “D” shape. • Hyperacute hemorrhage (within minutes) can appear hypodense on CT. • Acute hemorrhage is markedly hyperdense on CT in relation to muscle (blood will usually measure between 50 and 70 H.U). • Recent/subacute hemorrhage appears iso/hypodense, and an old clot will have similar CSF density as it liquefies. • On MR scan, the appearance of hemorrhage is dependent on the age of the hemorrhage and the stages of the clot, though it can be variable particularly in extracranial location like the orbit: • A fresh clot containing deoxyhemoglobin appears isohypointense on T1 and hypointense on T2 imaging; as it changes to methemoglobin, the signal becomes hyperintense from the periphery to the center of the hemorrhage, eventually producing a homogenous high signal. The intensity lessens as the methemoglobin breaks down to hemosiderin and ferritin.