<s>[INST] context: Retinoblastoma: 1 Most common Intraocular tumor of childhood. 2. Malignant primary neoplasm of retina that arises from neuroectodermal cells of retina (pigment layer). 3. May be a congenital lesion that is present but not usually apparent at bih; average age of diagnosis is 13 months. 4. Principle symptom = unilateral blindness. 5. Primary sign = Leukocoria. 6. It is bilateral in about 30% cases. 7. It is histologically composed of round cells with 'Rosette' pattern 8. Other round cell tumors include neuroblastoma, Ewing's sarcoma, NHL, etc. When bilateral, follows AD with complete penetrance pattern. Chromosome 13 mutation (100% in B/L and 15% in U/L). Histopathology: Flexner Wintersteiner rosettes. It is a PNET. Morphologic forms 1. Endophytic 2. Exophytic 3. Diffuse form Type based on location 1. Unilateral (70%) 2. Bilateral (30%) 3. Trilateral (<1%) ? Bilateral RB plus pineal or suprasellar tumor 4. Tetra/Quadrilateral (< 0.1%) ? Bilateral RB plus pineal and suprasellar mass. CT Scan Calcification--Intraocular mass centered posteriorly in globe with moderate or intense CT with punctate or finely speckled calcification (<90%) with or without extraocular extension. MRI: best for seeing extraocular extension. Treatment: 1. Small sized tumor - (plaque or ext. beam) with/without vitreous seeding 2. Large RB - local extension: Enucleation ? External beam . 3. Unilateral tumor without invasion has excellent prognosis. Coats disease - Increased density in all or pa of vitreous in normal sized globe without calcification. Congenital cataract - Vitreous normal, lens is dense. [/INST] question: The mother of a one and a half year old child gives history of increasing proptosis of left eye for the past 1 month. Examination revels left eye white reflex. On computed tomography scan of the orbit there is left orbital mass with calcification mainly centred within the globe. The most likely diagnosis is? | options: A: Congenital cataract B: Retinoblastoma C: Endophthalmitis D: Coats disease | answer: B </s>