Radiological Evaluation of Ocular Melanoma Metastasis - An Overview

Introduction

Ocular melanoma is a rare cancer of the eye that is said to affect about 5 people in a million adults. Although rare, it is the most common primary malignancy of the eye. Also called conjunctival melanoma. Primary cancers are those that originate at the site itself and are not spread from some other location. Less than 1 percent of patients suffering from ocular melanoma show metastasis to other regions of the body upon initial assessment. The liver is reported to be the most prevalent site where the cancer spreads, followed by bone and retroperitoneal nodules. It is an aggressive tumor and rapidly spreads to other parts of the body. Older adults are more susceptible to ocular tumors. However, it can occur at any age. The metastasis is very critical and may occur at a micro level as well. It is quite difficult to evaluate every micro metastasis location, and thus prognosis is questionable. Imaging the liver, lungs, and other potential sites makes it easier to identify the areas where the cancer has spread and assists in controlling the tumor effectively. This article aims to discuss the several imaging modalities adopted for this purpose and how ocular melanoma is evaluated radiographically.

Where Does Ocular Melanoma Metastasize?

Ocular melanoma has the ability to spread to other regions of the body quite rapidly than expected. 85 percent of all ocular melanomas originate in the uveal tract of the eye. This mainly comprises the iris, ciliary body, and choroid. The other 5 percent arise from the conjunctiva or other regions of the eye. Metastasis of ocular melanoma is usually seen after treatment cessation and a period of disease-free interval. The clinical and radiological evaluation of several ocular melanoma patients showed the following results:

1. Less than 1 percent of patients showed metastasis upon initial diagnosis of cancer. This indicates that metastasis seldom happens in the early stages of the illness.

2. Metastasis was found to occur in patients on an average of about three years after initial diagnosis. This encompassed the duration of original cancer treatment and a period of disease-free living prior to the detection of metastases.

3. A number of patients died between 1 and 38 months after initiation of the metastasis.

4. About 92 percent of patients showed hepatic metastasis, out of which 55 percent showed solely liver involvement initially.

5. Pulmonary parenchymal metastases are reported in about 31 percent of patients, out of which only 4 percent showed metastasis limited to the lungs.

6. Bone metastases, mostly involving the spine, were observed in 23 percent of patients.

7. Skin and subcutaneous involvement was observed in 17 percent of patients. However, only a handful of them showed skin metastases upon initial diagnosis.

8. Retroperitoneal nodules showed metastases in about 14 percent of patients and almost always accompanied hepatic metastases.

9. Very rarely, brain and adrenal metastases were also observed.

To summarize the above points, nearly all patients with metastatic ocular melanoma had hepatic involvement, and the liver is the most frequently involved initial location of metastatic involvement. After a protracted period without illness, metastases may appear.

How Is Ocular Melanoma Metastasis Diagnosed?

There are several imaging modalities used to identify the presence of ocular melanoma and to perform a thorough surveillance for any signs of metastases.

1. Computed Tomography (CT)

CT is the most preferred imaging modality for ocular melanoma metastases. CT has many well-known benefits, such as being widely accessible, having acceptable tolerability, having the capacity to quickly image the complete body, having fair picture quality, and having repeatable imaging properties. The imaging of the lungs is best achieved with the help of CT. However, it has a couple of drawbacks to make note of: CT uses ionizing radiation; it is unable to identify liver micro metastases that are <0.3 inches in size. The use of intravenous contrast-enhanced CT is implemented to identify metastases in the liver and other organs.

2. Magnetic Resonance Imaging (MRI)

Using an MRI successfully counteracts the limitations associated with CT scans. In particular, MRI is the imaging modality used for liver metastases. MRI evaluation of lesions less than 0.5 inch is far superior. Without a doubt, the standard imaging modality of CT may be replaced by improvements in MRI technology.

3. Positron Emission Tomography (PET-CT)

Another popular method for assessing melanoma metastases is PET-CT. With the aid of PET-CT, metastatic lung nodules larger than 12 mm can be easily identified. Metastases in the bone and lymph nodes are also quite easy to detect. PET-CT does, however, have disadvantages in relation to smaller metastases, particularly liver metastases, as compared to MRI. PET-CT also has the drawbacks of being relatively costly and not being widely accessible.

4. Ultrasound

One method for assessing melanoma metastases is ultrasound. On an ultrasound, liver metastases typically appear as hypoechoic nodules. However, a complete evaluation of the liver requires a lot of time and technical skill, especially in large individuals, and ultrasonography is very operator-dependent. Moreover, ultrasonography has very little use in the surveillance of malignancies other than liver-related ones. On the other hand, contrast-enhanced ultrasonography is clearly superior to conventional ultrasonography. However, its application is currently limited.

Metastases from melanoma typically appear one month to up to thirty-six years after the original diagnosis. Even after the treatment phase has ended, a comprehensive surveillance of metastases encompassing all locations, including the liver, bone, skin, and subcutaneous tissues, needs to be performed on a regular basis. The genetic profile and the tumor histology help determine when to start surveillance and how often one requires it.

Conclusion

It is clearly evident how important imaging is in determining the prognosis of an individual suffering from ocular melanoma. The prognosis for liver metastases is extremely poor, and the survival rate is much lower compared to when the metastases are present outside of the liver. When identifying the first metastasis and monitoring the lesions following therapy, the CT and MRI characteristics of these metastases are crucial. Since the primary factor affecting mortality rates is the presence or absence of liver metastases, it is imperative that the liver be thoroughly evaluated.