White matter: A good reference for the signal intensity evaluation in magnetic resonance imaging for the diagnosis of uveal melanoma

Abstract

Background: Comparing the signal intensity (SI) of an ocular mass to that of the vitreous body has been suggested. Most ocular lesions show a hyper-intense signal compared to the vitreous body on T1-weighted (T1w) images, and malignant melanomas have been almost always determined as 'cannot be excluded' in reports.

Purpose: This study aimed to determine the accuracy of magnetic resonance imaging (MRI) in the diagnosis of uveal melanoma by using normal white matter as reference tissue for SI evaluation on T1w images and vitreous body on T2w compared to the conventional method using the vitreous body as a reference on both T1w and T2w images.

Methods: The MRIs of 43 patients (between August 2006 and July 2018) sent to rule out uveal melanoma were blindly reviewed by two radiologists. By using white matter as a reference for SI evaluation on T1w images and vitreous body as a reference on T2w images, uveal melanomas were suggested by hyper-intense signal on T1w and hypo-intense signal on T2w with homogeneous enhancement. The accuracy of diagnosis of uveal melanoma using white matter as a reference on T1w was compared to the conventional method using the vitreous body as a reference on both T1w and T2w images.

Results: The diagnosis of uveal melanoma using white matter as a reference gave a sensitivity of 92.31% (95% confidence interval (CI) 63.97-99.81) and specificity of 100.0% (95% CI 88.43-100.0). By using the vitreous body as a reference, sensitivity as high as 100.0% (95% CI 100.0-100.0) was obtained, but specificity was low at 53.33% (95% CI 34.33-71.66).

Conclusions: White matter is a good reference for the diagnosis of uveal melanoma, with high sensitivity and much higher specificity than conventional methods using the vitreous body as a reference.

Keywords: Uveal melanoma; magnetic resonance imaging (MRI); reference; white matter.

Figure 1.

The typical magnetic resonance imaging (MRI) appearance of melanoma. A 67-year-old woman with blurred vision in the left eye for 10 days. (a) Axial T1-weighted spin-echo MRI (400/10.10) shows an ocular mass (*) with a hyper-intense signal compared to normal white matter (arrow). (b) Axial T2-weighted spin-echo MRI (3000/90) shows a hypo-intense mass (*) compared to the vitreous body. (c) Contrast-enhanced T1-weighted image (400/12) shows homogeneous enhancement.

Figure 2.

MRI of a 36-year-old man with known adenocarcinoma of the lungs who developed blurred vision in the left eye. (a) Axial T1-weighted spin-echo MRI (471/12) shows a hypo-intense mass. (b) Axial T2-weighted spin-echo MRI (3000/90) shows a hypo-intense mass. (c) Axial contrast-enhanced T1-weighted spin-echo MRI (551/12) shows enhancement intraocular mass and adjacent retrobulbar fat as evidence of extra-ocular invasion (arrow). Small metastasis with surrounding brain oedema in the right temporal lobe are noted (arrowhead).

Figure 3.

MRI of melanoma in a 51-year-old woman with blurred vision in left eye for one year. (a) Axial T1-weighted spin-echo MRI (400/9) shows the iso- to slightly hypo-signal intensity intraocular mass (arrow). (b) Fat suppressed T1-weighted spin-echo image (400/12). (c) Axial T2-weighted gradient-echo MRI (511/11, 18° FA) shows evidence of associated internal haemorrhage seen as a hypo-intense signal. (d) Post-contrast-enhanced fat-suppressed T1-weighted image (551/12) reveals moderate enhancement of the lesion.

Figure 4.

(a) Axial computed tomography image of the orbit in a five-year-old boy with left eye leukocoria for one month reveals total retinal detachment in the left eye without evidence of calcification. (b) Axial T2-weighted spin-echo MRI (396.46,11.51) shows a hypo-intense mass. (c) Axial contrast-enhanced T1-weighted spin-echo MRI (400/12) and (d) axial fat-suppressed contrast-enhanced T1-weighted spin-echo MRI (400/12) show slightly homogeneous enhancement mass (arrowhead).