Cellular Classification

Retinoblastoma is composed mainly of undifferentiated anaplastic cells that arise from the retina. Histology shows similarity to neuroblastoma and medulloblastoma, including aggregation around blood vessels, necrosis, calcification, and Flexner-Wintersteiner rosettes. Retinoblastomas are characterized by marked cell proliferation as evidenced by high mitosis counts and extremely high MIB-1 labeling indices.[1]

Cavitary retinoblastoma, a rare variant of retinoblastoma, has ophthalmoscopically visible lucent cavities within the tumor. The cavitary spaces appear hollow on ultrasonography and hypofluorescent on angiography. Histopathologically, the cavitary spaces have been shown to represent areas of photoreceptor differentiation.[2] These tumors have been associated with minimal visible tumor response to chemotherapy, which is thought to be a sign of tumor differentiation.[3]

1. Schwimer CJ, Prayson RA: Clinicopathologic study of retinoblastoma including MIB-1, p53, and CD99 immunohistochemistry. Ann Diagn Pathol 5 (3): 148-54, 2001.  [PUBMED Abstract]
   
   
2. Palamar M, Pirondini C, Shields CL, et al.: Cavitary retinoblastoma: ultrasonographic and fluorescein angiographic findings in 3 cases. Arch Ophthalmol 126 (11): 1598-600, 2008.  [PUBMED Abstract]
   
   
3. Mashayekhi A, Shields CL, Eagle RC Jr, et al.: Cavitary changes in retinoblastoma: relationship to chemoresistance. Ophthalmology 112 (6): 1145-50, 2005.  [PUBMED Abstract]