Bilateral retinoblastoma and pineal cyst with atypical MRI appearance

Clinical History

A 7-month-old boy with no family history of malignancy presented with bilateral leucocoria and left eye protrusion. He showed no signs of neurological dysfunction.

Imaging Findings

The ultrasound examination of the eyeballs showed bilateral mass lesions with calcifications. The MRI showed solid tumour formations in both globes, highly suggestive of bilateral retinoblastoma. Tumours showed fairly homogeneous enhancement after application of the gadolinium contrast medium and dropout of signal intensity on susceptibility-weighted imaging, which suggested calcifications. An 8 mm cyst within the pineal gland with enhancing, partially nodular thickening of the wall was, in the setting of bilateral retinoblastoma, highly suspicious for pineoblastoma. Subsequent MRI examinations during the course of the following 8 months showed significant growth of the pineal cystic formation (increased from 8 mm to 16 mm in diameter).

Discussion

Background: Retinoblastoma is the most common eye tumour in childhood and represents 3% of all tumours in children [1]. 35% of all retinoblastomas occur bilaterally [2, 3].

Clinical perspective: Ophthalmological signs and symptoms include reduced visual acuity, leucocoria, nystagmus, ophthalmoplegia, strabismus, glaucoma, microphthalmia and papilledoema [4].
Pineal cysts are associated with bilateral retinoblastoma in 8% [5], but are generally rare in children under 10 years of age [5]. Pineal cysts are usually asymptomatic.
Pineoblastomas may cause signs of increased intracranial pressure such as headache, nausea, vomiting, lethargy, irritability or somnolence [4].
A cystic lesion of the pineal region in a child with bilateral retinoblastoma should always raise suspicion of a pineoblastoma [2].

Imaging perspective: Typically, pineoblastomas are lobulated intra-axial masses with a T1- hyperintense nodular thickening of the wall, heterogeneous enhancement after administration of the gadolinium contrast medium and poor demarcation from the surrounding structures [2, 6, 7, 8]. Pineal cysts are usually homogeneous structures; hypointense on T1-weighted and hyperintense on T2-weighted and FLAIR sequences with respect to the surrounding structures [5]. The cyst wall is usually thinner than 2 mm and shows homogenous enhancement. Dilemma arises when the cyst wall is thicker than 2 mm or indicates nodular thickening, and the cyst is enhanced heterogeneously and not only marginally [1, 7]. Pineal cysts are characterised by stagnation or slow growth over a range of many years [5]. The most reliable radiological sign of malignancy of the pineal lesion is a significant increase in diameter compared to the previous MR examination [9].

Outcome: Suspicion of pineoblastoma in our case was high due to significant growth and an atypical enhancing pattern of the pineal cystic formation. Neurosurgical excision of the suspected pineoblastoma was performed. Histologic examination revealed normal pineocytes without abnormal mitoses and occasional colloidal inclusions, consistent with the diagnosis of the pineal cyst.

Teaching points: Our case highlights the importance of a distinction between pineal cyst and pineoblastoma in the setting of bilateral retinoblastoma. In spite of an atypical enhancement pattern and significant growth of the cystic lesion over the relatively short period of 8 months, the lesion in our case proved to be a simple cyst. Standard radiological parameters of malignancy of pineal lesions failed to suggest the correct diagnosis. Further studies of pineal gland cyst characteristics in the setting of bilateral retinoblastoma could improve the specificity of the imaging.

Differential Diagnosis List

Final Diagnosis

Bilateral retinoblastoma and pineal cyst with atypical MRI appearance

URL:	https://eurorad.org/case/15105
DOI:	10.1594/EURORAD/CASE.15105
ISSN:	1563-4086