Proptosis

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Proptosis refers to forward protrusion of the globe with respect to the orbit. There are many causes of proptosis which can be divided according to location and it is worth remembering that its not just orbital disease processes that cause proptosis.

Terminology

Exophthalmos also describes forward protrusion of the globe. Several authors use the terms differently, which can be confusing:

proptosis and exophthalmos used interchangeably
exophthalmos used to refer to severe (over 18 mm) proptosis ⁵
exophthalmos used to refer to endocrine-related proptosis ⁶

Radiographic features

CT

Assessment of proptosis on cross-sectional imaging is difficult and dependant on the study being acquired in the correct plane:

the plane of the study must be parallel to the head of the optic nerve and the lens
the patient must have their eyes open and be looking forward with no eye movement

The reference line for measurement of proptosis is the interzygomatic line (a line is drawn at the anterior portions of the zygomatic arches):

the distance from this line to the posterior sclera is normally 9.9 +/- 1.7 mm ²
the distance from this line to the anterior surface of the globe should be less than 23 mm ⁴

The thickness of the extra-ocular muscles can also be used ¹.

MRI

MRI may also be used in evaluation due to its multiplanar and the inherent contrast capabilities. Use of MR prevents ionizing radiation to orbits. The imaging findings are similar as described above for CT.

Differential diagnosis

The differential diagnosis of proptosis is broad and includes a wide range of mass lesions that originate within the cranium, sinuses, paranasal spaces and orbit ³:

thyroid orbitopathy
infection
tumour
- lymphoma, e.g. orbital lymphoma
- meningioma, e.g. sphenoid wing meningioma
- glioma
- orbital metastasis
trauma, e.g. iatrogenic, post-surgical
vascular lesions
orbital inflammatory syndrome (a.k.a. orbital pseudotumour)
pseudoproptosis

-</ul><p>The thickness of the <a href="/articles/intraocular-muscles">intraocular muscles</a> can also be used <sup>1</sup>.</p><h4>Differential diagnosis</h4><p>The differential diagnosis of proptosis is broad and includes a wide range of mass lesions that originate within the cranium, sinuses, paranasal spaces and orbit <sup>3</sup>:</p><ul>
+</ul><p>The thickness of the <a title="Extra-ocular muscles" href="/articles/extra-ocular-muscles">extra-ocular muscles</a> can also be used <sup>1</sup>.</p><h5>MRI</h5><p>MRI may also be used in evaluation due to its multiplanar and the inherent contrast capabilities. Use of MR prevents ionizing radiation to orbits. The imaging findings are similar as described above for CT.</p><h4>Differential diagnosis</h4><p>The differential diagnosis of proptosis is broad and includes a wide range of mass lesions that originate within the cranium, sinuses, paranasal spaces and orbit <sup>3</sup>:</p><ul>
~~-<li><a title="Optic nerve glioma" href="/articles/optic-nerve-glioma">glioma</a></li>~~
+<li><a href="/articles/optic-nerve-glioma">glioma</a></li>
~~-<li><a title="Orbital venous varix (OVV)" href="/articles/orbital-venous-varix">orbital varix</a></li>~~
+<li><a href="/articles/orbital-venous-varix">orbital varix</a></li>

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