Defining Vitreoretinal Lymphoma
Primary Vitreoretinal Lymphoma (PVRL) is a subtype of Central Nervous System Lymphoma (CNSL). Invasion of the central nervous system is common, occurring in 16-34% of cases at onset and 35-90% of cases during the clinical course of the disease. On the other hand, 15-25% of the patients with PCNSL develop VRL (Grimm et al, 2007, 2008).
As a central database for this rare disease does not exist, the rate of occurrence of PVRL is unclear. Currently, the construction of a multicenter VRL registry within Japan has allowed for the practice of epidemiological studies.
A 20-year retrospective study conducted at a large hospital in Canada reveals that the incidences of VRL in British Columbia from the year 1990 to 2010 have been 0.017-0.048 cases per 100,000 people（Levasseur et al, 2013). In Japan, the number of patients with PVRL has exhibited an upward trend, with the national survey observing 1.0% cases of PVRL among first-time uveitis patients in 2002 and approximately 1.9% in 2009.
PVRL generally affects adults in their thirties to eighties, with 63 as the median age of diagnosis and no gender ratio (Grimm et al, 2007).
The pathophysiology of CNS invasion due to PVRL remains a matter of debate. One theory states that the subclinical CNS invasion of brain legions exists from the initial stage but is undetected by Magnetic Resonance Imaging (MRI). Another theory proposes that the CNS invasion is disseminated through microinvasion from the eye to the brain through the retina and optic nerve. Experiments utilizing a mouse model support the latter hypothesis that CNS disseminated from the retinal pigment epithelium to the choroid coat. Elevated levels of IL-10 in the cerebrospinal fluid have also been confirmed in PVRL patients without CNS metastasis.