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|Year : 2015 | Volume
| Issue : 4 | Page : 564-566
Intraventricular silicone oil mimicking a colloid cyst
Mahavir P Swami, Kanta Bhootra, Chintan Shah, Bhavik Mevada
Department of Radiology, Shree B.D. Mehta Mahavir Heart Institute, Shree Mahavir Health Campus, Surat, Gujarat, India
|Date of Web Publication||4-Aug-2015|
Mahavir P Swami
M-1104, Jolly Residency, Vesu Main Road, Vesu, Surat, Gujarat
Source of Support: None, Conflict of Interest: None
We report a case where intraventricular migration of silicone oil occurred into the third ventricle, mimicking the presence of a colloid cyst. To the best of our knowledge, this is the first case reported where intraventricular silicone oil (SiO) presented at the foramen of Monro, resembling the radiological appearance of a colloid cyst. The systemic dissemination of silicone oil is a very rare complication of intravitreal SiO administration that is used for providing a mechanical tamponade that maintains the retinal attachment following repair of a retinal detachment. The imaging findings that are characteristic of the presence of intraventricular silicone oil are its usual dissemination in a nondependent location and the accompaniment of changes in its location based on changes in the patient's position.
Keywords: Colloid cyst; foramen of Monro lesions; intraventricular silicone oil; silicone oil
|How to cite this article:|
Swami MP, Bhootra K, Shah C, Mevada B. Intraventricular silicone oil mimicking a colloid cyst. Neurol India 2015;63:564-6
| » Introduction|| |
Silicone oil (SiO) is used as a long-term endotamponade agent in the management of complicated retinal detachments. Intraventricular migration is an unusual complication that occurs following the intravitreal administration of SiO.  Magnetic resonance imaging (MRI) and computed tomography (CT) are useful modalities for diagnosing an intraventricular SiO. This condition is usually an incidental finding following treatment that may occur in patients with glaucoma or optic atrophy. The majority of the cases are asymptomatic. 
| » Case Report|| |
A 68-year-male presented with a history of fever, loss of bladder control and delusions for 2-3 days. He was a known case of type II diabetes mellitus for more than 25 years. He had diabetic nephropathy and neuropathy for 8-10 years. His diabetic retinopathy was diagnosed 15 years back. He had a retinal detachment due to proliferative retinopathy in both the eyes at an interval of 1 year, for which he was treated with intravitreal SiO injections 9 and 10 years back with a poor visual outcome. On examination, he had no vision in both the eyes except light perception.
On the day of admission, he was agitated and febrile. His blood pressure was 100/70 mm of Hg. His urinary bladder was distended and needed catheterization. His complete blood count showed neutrophilia, (a white blood cell [WBC] count of 15400/cmm with 80% neutrophils). His serum electrolytes were normal, but random blood sugar was 320 mg/dl, serum creatinine 2.4 mg/dl, and C-reactive protein (CRP) 24 mg/dl. His routine urine report showed 15-20 WBCs/high power field. The urine culture was sent. Before planning a lumbar puncture to rule out meningitis, a computed tomography (CT) of the brain was done.
An unenhanced helical CT brain was performed with coronal and sagittal reformations. The CT scan showed hypodense chronic ischemic areas in bilateral centrum semiovale, corona radiata, and periventricular white matter with mild generalized cerebral and cerebellar atrophic changes. A small abnormal well-defined, rounded, hyperdense lesion was seen in the anterosuperior part of the third ventricle, near the foramen of Monro with a density of 50-60 HU. Similar hyperdense material, with a mean density of 50-60 HU, was seen in bilateral globes, in a nondependent part. Due to the location of the hyperdense lesion, a differential diagnosis of colloid cyst and intraventricular SiO was suggested [Figure 1].
|Figure 1: (a) Axial, (b) coronal, and (c) sagittal reformatted images show the small abnormal rounded hyperdense area in the anterosuperior part of the third ventricle, near the foramen of Monro. Similar abnormal nondependent hyperdense material is also seen in bilateral globes|
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A lumbar puncture was also carried out. The cerebrospinal fluid (CSF) opening pressure was normal. The CSF report showed a normal cell count and biochemistry.
There was further deterioration of the patient's consciousness status over a period of 48 h; hence, a follow up CT scan was suggested. The repeat CT showed two small nondependent hyperdense lesions within the frontal horns of both lateral ventricles. The hyperdense lesion, seen at the foramen of Monro in the previous CT scan, was not visualized on the repeat CT images, thus pointing towards an intraventricular migration of SiO and not the presence of a colloid cyst. The hyperdense material in bilateral globes was persistent [Figure 2].
|Figure 2: Follow-up computed tomography (a) and (b) axial and (c) sagittal reformatted images show migration of the abnormal hyperdense material from the anterosuperior part of the third ventricle, near the foramen of Monro to the nondependent part of frontal horns of bilateral lateral ventricles|
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The patient made an uneventful recovery with antibiotics (as per urine culture report), proper blood sugar control, and hydration.
| » Discussion|| |
Intravitreal SiO is injected to provide a mechanical tamponade that maintains retinal attachment following repair of a retinal detachment.  On CT images, the intraventricular silicone appears as a hyperdense mobile nodule in a nondependent position. The signal intensity characteristics on MRI are variable and depend on the sequence parameters, field strength, and viscosity of SiO.  MRI is diagnostic of an intraventricular silicone, which is typically hyperintense on T1-weighted images, when compared with the normal CSF or vitreous, and is heterogeneously iso-, hypo- or hyper-intense on T2-weighted images. Chemical shift artifacts on MRI may help in establishing the diagnosis of an intraventricular SiO. 
Our case is unusual as this is the first case where the intraventricular silicone presented at the anterosuperior part of the third ventricle near the foramen of Monro, mimicking a colloid cyst. A follow-up CT scan after 2 days showed a change in the location of silicone in a nondependent part (frontal horns) of both lateral ventricles.
The differential diagnosis of a hyperdense lesion at the foramen of Monro include a colloid cyst, calcified or hyperdense meningioma, giant cell astrocytoma, ependymoma, choroid plexus papilloma and hemorrhage. Of these, colloid cyst is the most common lesion. , Intraventricular silicone can also mimic an intraventricular hemorrhage. Intraventricular silicone may be distinguished from hemorrhage as silicone tends to stay in the nondependent portion of the ventricle. 
Complications of an intravitreal SiO injection include entry of SiO into the anterior chamber and the subretinal region. Other complications include biomicroscopically visible SiO emulsification, keratopathy, glaucoma, closure of the inferior iridectomy, and reproliferation of epiretinal and subretinal fibrous membranes.  Intracranial migration of SiO through the optic nerve posterior to the lamina cribrosa to the optic chiasm and brain is an uncommon route of its dissemination. 
The pathway that allows the transit of silicone from the vitreous to the CSF is uncertain. There is no normal anatomic communication between the vitreous and the subarachnoid space.  It has been hypothesized that silicone may have entered the atrophic optic disc due to the raised intraocular pressure. , The intraneural silicone then coalesced and extended posteriorly, eventually migrating into the subarachnoid space that surrounds the optic nerve. Communication of the subarachnoid space that surrounds the optic nerve with the intracranial subarachnoid space would then allow the passage of silicone into the ventricles. This theory is supported by case reports that demonstrate the extension of intravitreal silicone into the intraorbital optic nerve. , In the absence of glaucoma and optic nerve abnormalities, the risk of extraocular SiO penetration is so low that the technique of SiO endotamponade being performed in patients with a complex retinal detachment does not need to be modified.  In a patient with glaucoma or optic atrophy, after SiO injection, a CT/MRI brain should be done to rule out the possibility of intracranial migration of SiO. 
Currently, there is no consensus on the surgical removal of intraventricular SiO, and the patients have been asymptomatic in the vast majority of cases reported in the literature.  A case report has described a patient who had an intravitreal SiO migration into the cerebral ventricles and presented with chronic headache and elevated opening pressure on lumbar puncture. There was complete resolution of symptoms after a ventriculoperitoneal shunt placement. 
| » References|| |
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[Figure 1], [Figure 2]
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