Imaging in Coats disease
On scanograms, Coats disease exhibits a number of pathognomonic imaging characteristics. The main substrate of the disease is massive lipoprotein exudate.
- Orbit CT (axial projection): clear visualization of posterior hyaloid membrane detachment. The posterior hyaloid space is filled with pathological content.
- Orbit MRI (T1-WI, sagittal projection): the accumulated lipoprotein exudate produces a pronounced hyperintense (bright) signal, allowing reliable identification of the nature of the effusion.
- Morphometric changes: the affected eyeball is typically reduced in size, forming microphthalmia.
Differential diagnosis: pathologies with retinal detachment
Coats disease requires differential diagnosis with other conditions causing retinal detachment and altered eyeball dimensions.
Persistent hyperplastic primary vitreous (PHPV)
In this pathology, the primary vitreous undergoes abnormal regression. A band-like fibrovascular structure forms between the posterior lens capsule and the retina (the central hyaloid artery may persist within it).
Imaging features of PHPV:
- Presence of a linear, cone-shaped, or band-like partition extending from the lens to the retina.
- Axial slices show a V-shaped retinal detachment tightly anchored at the ora serrata and the optic disc.
- The primary vitreous may enhance with contrast medium (on contrast-enhanced CT).
- MRI (T2, axial) demonstrates a hypointense retrolenticular fibrovascular strand, while T1 (sagittal) shows a hyperintense subretinal hemorrhage.
- In fresh hemorrhages, CT/MRI reveals fluid-fluid levels.
The disease is often accompanied by microphthalmia, posterior lens capsule defect (leading to cataract), and secondary retinal detachment. Disease progression may lead to eyeball subatrophy (phthisis bulbi).
Retinopathy of prematurity (retrolenticular fibroplasia)
This condition occurs secondarily due to excessive oxygen therapy in premature infants. Retinal vascular development arrests, followed by disorganized resumption of growth. Newly formed vessels and fibrous tissue contract, causing retinal detachment. The incidence of this pathology is decreasing thanks to surfactant therapy. Brain MRI may concurrently reveal periventricular leukomalacia.
Disorders of eyeball size and shape
Since Coats disease is closely associated with alterations in visual organ dimensions, imaging evaluation requires assessing for bilaterality to identify the affected side.
- Microphthalmia: an abnormally small eyeball (accompanied by a reduced bony orbit in congenital cases). Causes: Coats disease, PHPV, coloboma, infections, trauma, radiation therapy.
- Macrophthalmos: generalized enlargement of the eyeball. A frequent cause is myopia (axial elongation). It is associated with collagenoses (Marfan, Ehlers-Danlos syndromes) and homocystinuria.
- Buphthalmos: enlargement of the eye due to high intraocular pressure in children (elastic sclera). Associated with pediatric glaucoma and neurofibromatosis type 1. Requires differentiation from exophthalmos.
- Anophthalmia: true (complete absence of optic vesicle development) or clinical (absence of a detectable globe on T1-weighted MRI in the presence of adnexa).
- Staphyloma: focal outpouching of the sclera (more commonly posterior, temporal to the optic disc). Associated with myopia, trauma, or infection.
Other orbital pathologies
When analyzing orbital imaging, it is important to distinguish exudative processes from other masses and deposits:
- Drusen: deposits of lipoproteinaceous material between the retinal pigment epithelium and Bruch's membrane. On CT, they appear as small, often bilateral foci of calcification in the optic nerve head (ONH) region. They can mimic ONH edema on ophthalmoscopy.
- Coloboma: congenital anomaly of the ONH (ranging from optic pits to morning-glory syndrome — morning-glory papilla). Involves the retina, choroid, and iris. Imaging methods play an auxiliary role. May be associated with CHARGE syndrome.
- Dermoid: the most common congenital orbital mass (ectodermal inclusion). Located extraconal (frontozygomatic or frontoethmoidal suture). On CT/MRI, the key feature is fat density/signal, with potential fat-fluid levels and calcifications. Causes bone remodeling.
To remember the associations of microphthalmos: "C-P-C" — Coats, PHPV, Coloboma — the classic triad of causes of an abnormally small eyeball on imaging.
Class and exam questions
How does the lipoproteinaceous exudate in Coats' disease appear on MRI?
On T1-weighted images (especially in the sagittal plane), the accumulation of lipoproteinaceous exudate is characterized by a hyperintense (bright) signal.
What is the main anatomical defect detected on orbital CT in Coats' disease?
Axial CT scans visualize posterior hyaloid membrane detachment and pathological filling of the posterior hyaloid space.
How to differentiate PHPV from other causes of retinal detachment on imaging?
Pathognomonic for PHPV is the presence of a linear fibrovascular membrane extending from the posterior surface of the lens to the retina and a V-shaped retinal detachment tightly fixed at the ora serrata and the optic nerve head.
With a change in which eyeball size is Coats' disease associated?
Coats' disease is accompanied by microphthalmos—an abnormal reduction in the size of the affected eyeball.
What else to study on this topic
- Imaging findings and complications of PHPV (Persistent Hyperplastic Primary Vitreous)
- Pathogenesis and neuroimaging in retinopathy of prematurity
- Differential diagnosis of eyeball size disorders (buphthalmos, macrophthalmos, anophthalmia)
- CT features of optic disc drusen and their differentiation from optic disc edema
- Extraconal orbital masses: dermoid cysts and their characteristics
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