Hypermature cataract is an extremely advanced lens opacity in which a mature cataract progresses, the cortex becomes hyperosmotic, and water flows in. Because the opacity is severe, direct observation of the fundus becomes difficult, and ultrasound examination is necessary to evaluate intraocular structures.
In rare cases during this ultrasound examination, a hypermature cataract can produce a dome-shaped artifact that mimics uveal melanoma. This is called “cataract-induced pseudomelanoma,” which is not actually a tumor but a false depiction of the lens equator due to the scanning angle of the ultrasound probe.
In a large study published by Shields et al. in 2005, among 12,000 cases referred for suspected uveal melanoma, 1,739 cases were pseudomelanomas. Of these, only 10 were due to cataract. In a 2013 report by the same group, 20 cases in which hypermature cataract mimicked uveal melanoma were detailed.
Uveal melanoma is the most common primary intraocular malignancy in adults, with an incidence of approximately 5.1 per million people per year (about 1,500 cases annually in the United States). About 85% occur in the posterior choroid and have a high risk of metastasis, requiring prompt and accurate diagnosis. This makes proper differentiation of pseudomelanomas even more important.
It is a state where a mature cataract progresses further, the cortex becomes hyperosmotic, and water flows in. The lens capsule becomes tense, and the opacity becomes extremely severe, making fundus visualization very difficult. The only treatment for cataract is surgery, and hypermature cataract is one of the cases with high surgical difficulty.
The main complaint is visual impairment due to hypermature cataract.
This disease (pseudomelanoma) itself has no specific subjective symptoms. The essential issue is that it is discovered incidentally on ultrasound examination.
True Melanoma
B-mode findings: Dome-shaped or mushroom-shaped mass. Accompanied by choroidal excavation and subretinal fluid.
A-mode findings: Low to moderate internal reflectivity, regular internal structure, high sound attenuation, presence of vascular pulsations.
Distribution: Single quadrant lesion. Corresponds to a specific anatomical site.
Pseudomelanoma
B-mode findings: Uniform oval or dome-shaped morphology. Hyperechoic cortical rim and hypoechoic core. Absence of vascular pulsations.
Changes with probe position: Changing the angle of the probe alters the morphology of the lesion.
Four-quadrant sign: When the ultrasound probe is angled obliquely, similar artifacts are observed in all four quadrants.
In a 2013 study by Shields et al., 2 of 20 cases had a luxated lens, observed as an oval or dome-shaped mass on the retinal surface. The lens was confirmed to move with changes in body position. In the 18 cases with anatomically normal lens position, oblique positioning of the ultrasound probe was found to depict the lens equator adjacent to the ciliary body in a melanoma-like fashion.
If a similar dome-shaped structure is observed in all four quadrants when the ultrasound probe is scanned obliquely, pseudomelanoma is strongly suspected. Additionally, the combination of absence of vascular pulsation, uniform elliptical shape, and a hyperechoic cortical rim is characteristic of pseudomelanoma. Final confirmation is obtained when the lesion disappears after cataract surgery.
Uveal pseudomelanoma due to hypermature cataract occurs due to a combination of the following factors.
Causes of hypermature cataract itself include aging, metabolic diseases (such as diabetes), trauma, inflammation, and radiation exposure. It can reach a hypermature state if cataract surgery is not performed for a long time.
In hypermature cataracts, optical biometry is difficult, so B-mode ultrasound is standardly used. Ultrasound measurement is recommended when optical measurement is impossible in mature or dense cataracts (ESCRS guidelines).
In B-mode examination, a probe is placed on the eyelid skin to image the interior of the eye. The resolution is 300 to 600 micrometers, making it suitable for observing the posterior segment and orbit.
| Finding | Pseudomelanoma | True melanoma |
|---|---|---|
| Vascular pulsation | Absent | Present |
| Confirmation in 4 quadrants | Possible | Not possible |
| Probe conversion | Morphological change present | Minimal change |
The core of differentiation is to convert the probe from a vertical to an oblique direction and check whether the same lesion is confirmed in all four quadrants.
Used for measuring axial length (preoperative assessment for cataract surgery). Also used to evaluate internal reflectivity and acoustic attenuation of lesions. True uveal melanoma shows characteristic acoustic attenuation (acoustic solidity).
Definitive diagnosis is obtained when the lesion disappears after cataract surgery (phacoemulsification).
With the patient’s eyes closed, gel is applied to the probe and the examination is performed over the eyelid. The patient is asked to move their eyes while the probe is adjusted to be perpendicular to the target tissue. Multiple scans, such as transverse and macular longitudinal views, are combined to evaluate the morphology, location, and mobility of the lesion.
There is no specific treatment for uveal pseudomelanoma caused by hypermature cataract. This condition is essentially an ultrasound artifact, and treating the cataract is the fundamental approach.
Phacoemulsification is performed for hypermature cataracts. The disappearance of the “pseudo-mass” on ultrasound after surgery also has diagnostic significance.
Hypermature cataract surgery is technically challenging. The nucleus is often very hard and the lens capsule fragile, so surgery by an experienced surgeon is recommended.
If surgical risk is high or the patient’s general condition is poor, careful observation may be an option. In such cases, regular ultrasound examinations are performed to monitor changes in artifacts.
Hypermature cataract is a condition in which the cortex of a mature cataract becomes hyperosmotic and water flows in. The lens capsule becomes tense, and the internal lens material liquefies. The nucleus often remains hard.
The lens is located behind the iris and is fixed to the ciliary body by zonules. The lens is involved in adjusting refractive power for near and far vision. Lens fibers are continuously produced throughout life, with old fibers forming the nucleus and new fibers forming the cortex. Transparency is maintained by the absence of organelles, but this also makes the lens vulnerable to oxidative stress.
In B-mode ultrasound, sound waves of 10–20 MHz interact with tissues to produce echoes, and images of hyperechoic or hypoechoic areas are constructed based on echo intensity.
When the probe is positioned obliquely, the equatorial lens adjacent to the ciliary body receives sound waves from the ultrasound probe, forming a dome-shaped artifact posteriorly. This is mistaken for a tumor-like lesion of the fundus. This “pseudo-mass” is characteristically observed similarly in all four quadrants, reflecting the anatomical presence of the lens circumferentially.
If the lens is dislocated, the dislocated lens itself is observed as a dome-shaped mass on the retinal surface.
Regarding uveal pseudomelanoma caused by hypermature cataract, improvements in diagnostic accuracy are expected due to advances in imaging diagnostic technology.
Ultrasound biomicroscopy (UBM) uses frequencies of 30–60 MHz to obtain high-resolution images with a depth of about 4–5 mm and a resolution of 50 micrometers, and is useful for detailed evaluation of the anterior segment and ciliary body. By more precisely depicting the relationship between the lens equator and ciliary body in cases of hypermature cataract, it may contribute to distinguishing artifacts from true lesions.
Furthermore, the use of multimodal imaging combining anterior segment optical coherence tomography (AS-OCT) and ultrasound is a future challenge.
