by Dr Noreen Norfaraheen Lee Abdullah MD (UKM), MMed Radiology (UKM), AM(Mal)

Answer to Case Of the Month 
Left (eye) retinoblastoma with intraconal and extraconal extension.

Discussion of Findings
The left eye is proptosed. Within the left globe, there is a heterogenously enhancing soft tissue mass. The mass has irregular margins. Multiple small foci of calcification are seen within. There is retinal detachment of the left eye. The extraocular muscles, the left optic nerve and the left eyelid are thickened. This would indicate involvement by the primary lesion. Left retro orbital fat is streaky and indicates involvement as well. The right orbit is normal.

Retinoblastoma is the most common intraocular malignancy of childhood. This tumor is congenital but not necessarily recognized at birth. The average time of diagnosis is 18 months. The disease has an autosomal dominant inheritance of variable penetrance. In familial cases, it tends to be bilateral. Typical presentation is leukokoria, strabismus, glaucoma and vision loss. Atypical presentation includes orbital cellulitis, ophthalmitis, conjunctivitis and systemic illness. Differential diagnosis include Coat’s disease, persistent hyperplastic primary vitreous and toxicariasis.

Retinoblastoma arises in the nuclear layer of the retina. It grows rapidly and invades adjacent tissues. As it outgrows its blood supply, cell necrosis occurs. There is a tendency to form a calcified complex. This calcification is easily detected radiologically. The malignant cells disseminate through the eye and implants at other sites like the choroids, retina and posterior surface of the cornea. It can also extend along the perineural and perivascular spaces and result in intraorbital and optic nerve spread of the tumor. Malignant cells also may be disseminated via the subarachnoid space surrounding the optic nerve and enter the central nervous system. Involvement of the intraorbital vascular system by the tumor permits spread to distant sites such as the long bones, viscera and lymphatics.

CT scan of the orbits is the imaging modality of choice in the investigation of retinoblastoma. Features that are unique to retinoblastoma will be the presence of a soft tissue mass with calcification involving the retina within the globe. The mass is usually dense mainly due to hemorrhage or calcification. CT is known to be superior in detecting calcification. Retinal detachment is also another associated finding. Thickening of the optic nerve sheath indicates extension of the tumor into the perineural subarachnoid space. When performing CT orbits for cases of retinoblastoma, it is important to image the brain as well as there may be intracerebral metastases and the rare trilateral retinoblastoma (bilateral retinoblastoma with an associated pineal gland tumor).

MRI is also a very useful adjunct study. The multiplanar capability and the superior soft tissue discrimination make MR a valuable tool for the evaluation of the intraorbital and/or intracranial extension of the retinoblastoma. MRI is more specific in detecting optic nerve involvement.
 

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Last Updated:
Tuesday, 04 January 2005