Tumours of the retina /retinoblastoma/.
Retinoblastoma is a malignant tumour of early childhood that develops from immature retinal cells. It can be unilateral or bilateral and the overall mean age at diagnosis is 18 months with no sex predisposition.
Retinoblastoma gene has been identified as 14 band on the long-arm of chromosome 13 (13q 14) and is a cancer suppressor gene. Deletion or inactivation of this protective gene by two mutations results in the occurrence of retinoblastoma. It has autosomal dominant inheritance; however, sporadic (non-hereditary) cases occur by somatic mutation.
Retinoblastoma arises as malignant proliferation of the immature retinal neural cells called, retinoblasts, which have lost both antioncogenic genes.
Signs and Symptoms:
The most common and best known initial clinical sign is a white pupillary reflex, called leukocoria. It is due to reflection of light from the yellow-white mass in the retrolental area. Other symptoms include:
- A squint which is usually convergent.
- Nystagmus which is seen in bilateral cases.
- Severe pain due to increased intraocular pressure
- Orbital cellulitis.
Some signs include: presence of multiple polypoid masses in the fundus and spread of tumour mass into the vitreous cavity.
Types of retinoblastoma:
- Glioma exophytum: the tumour grows outwards separating the retina from the choroid. It resembles detachment of the retina.
- Glioma endophytum: the tumour grows inwards towards the vitreous.
Stages:
The four clinical stages of retinoblastoma development include:
Stage 1: The quiescent stage—It lasts from six months to one year.
Stage 2: The glaucomatous stage—There is enlargement of the globe, proptosis and severe pain associated with raised intraocular tension.
Stage 3: The stage of extraocular extension—The tumour bursts through the limbus followed by rapid growth.
Stage 4: The stage of metastasis—The tumour spreads by the:
- i. Lymphatics—Preauricular and cervical lymph nodes.
- ii. Direct extension—Cranial and other bones. Optic nerve and brain. iii. Bloodstream—It spreads by choroidal vessels. Most common sites are bone and liver.
Differential diagnosis: Several other disorders should be excluded by ophthalmoscopy. For example, various conditions other than retinoblastoma which present as leukocoria are collectively called as ‘pseudoglioma’ so should therefore be distinguished from retinoblastoma; these are: congenital cataract, inflammatory deposits in vitreous following a plastic cyclitis or choroiditis, coloboma of the choroid, the retrolental fibroplasia (retinopathy of prematurity), persistent hyperplastic primary vitreous, toxocara endophthalmitis and exudative retinopathy of Coats. Exophytic retinoblastoma should be differentiated from exudative retinal detachment.