Scleral staphyloma

Radiological presentation of scleral staphyloma

During computed tomography (CT) in patients with severe myopia, characteristic changes of the eyeball can be detected. First, a marked axial elongation of the eyeball is visualized, which is the root cause of myopic refraction. Second, a key radiological sign of staphyloma is focal outpouching (from English outpouching) of the posterior sclera. Topographically, this formation is always located strictly lateral to the optic nerve head. Such a picture leaves no doubt about the presence of myopic staphyloma.

Optic disc drusen

When analyzing scans of the posterior pole of the eye, it is important to pay attention to the state of the optic nerve itself. One of the frequent findings is optic disc drusen (Drusen). On computed tomography, they are clearly visualized as bilateral calcified foci (calcific foci). These microcalcifications are located directly in the area of the optic nerve heads and can simulate papilledema during ophthalmoscopy, so CT confirmation of their presence is crucial.

Thyroid eye disease (thyroid orbitopathy)

As part of the differential diagnosis of exophthalmos (which can simulate eye enlargement in myopia), it is extremely important to know the signs of thyroid orbitopathy (Thyroid Orbitopathy).

This disease can clinically manifest even before the appearance of symptoms of thyroid gland damage itself. Statistically, women are affected four times more often than men (F:M ratio is 4:1), and the peak incidence occurs in the fourth and fifth decades of life. Thyroid eye disease is the most frequent cause of both bilateral and unilateral exophthalmos (proptosis). It is important to remember that bilateral involvement is much more common, and a clinically "unilateral" exophthalmos upon detailed imaging often turns out to be simply an asymmetric bilateral process.

The histological basis of the pathology is the deposition of mucopolysaccharides (predominantly hyaluronic acid) within the extraocular muscles. On CT and MRI (in STIR mode), this manifests by the following signs:

• Bilateral exophthalmos.
• Classic sign: fusiform (fusiform) thickening of extraocular muscles, in which the muscle tendons remain completely intact (sparing of the muscular tendon).
• Increase in the volume of intraorbital adipose tissue.
• Stranding of the adipose tissue (fat stranding), which gives the orbital fat a characteristic "dirty" (dirty) appearance on scans.
• Thickening of the soft tissues of the eyelids.

Rule of extraocular muscle involvement

In thyroid orbitopathy, there is a strict pattern of extraocular muscle involvement in the pathological process. In descending order of frequency, the muscles are arranged in the following sequence:

1. Inferior rectus muscle (inferior rectus).
2. Medial rectus muscle (medial rectus).
3. Superior rectus muscle (superior rectus).
4. Lateral rectus muscle (lateral rectus).

Clinical rule: isolated involvement of only the lateral rectus muscle is extremely rare. If you see thickening of only this muscle on CT, you must immediately begin searching for an alternative diagnosis.

Idiopathic orbital inflammation

One of the alternative diagnoses in orbital pathology is idiopathic orbital inflammation (Idiopathic Orbital Inflammation — IOI), also known by the synonym idiopathic orbital pseudotumor (idiopathic orbital pseudotumour).

This is a non-infectious disease of completely unknown etiology. Unlike thyroid orbitopathy, it has no clear gender predilection and can affect people of absolutely any age, although the statistical peak incidence also occurs in the fifth decade of life. This is one of the most frequent causes of orbital pathology in adult patients.

Class and exam questions

What else to study on this topic

• Morphological changes of the retina in the staphyloma zone
• MRI protocols (STIR mode) in orbital pathologies
• Differential diagnosis of idiopathic pseudotumor and orbital cellulitis
• Relationship of thyroid orbitopathy with thyroid hormone levels
• Surgical and conservative treatments for severe endocrine ophthalmopathy

Other topics in the Neuroimaging section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.