Seizure After Sudden Headache in a 16-Year-Old Cyclist

Payman Vahedi, MD; Zahra Mohajernezhad, MD; Mohammad Faraji-Rad, MD


March 25, 2022


The new onset of headache with nausea, vomiting, blurred vision, and diplopia were strongly suggestive of increased intracranial pressure in this patient. The presence of bilateral sixth nerve palsy and bilateral papilledema on neurologic examination confirmed this suspicion. Laboratory tests revealed normal electrolytes, renal function, and complete blood cell count findings. The CT scan of the brain revealed acute lateral ventricular hydrocephalus, with periventricular edema and a hyperdense round mass within the third ventricle causing obstruction of the foramen of Monro. The most likely diagnosis was colloid cyst of the third ventricle.

Colloid cysts of the third ventricle account for 10%-15% of intraventricular tumors. They are the most common masses of the third ventricle found in adults. Controversy exists over whether these cysts can be classified as brain neoplasms. The cysts are considered to be congenital in origin, and familial occurrence of the disease has been reported[1,2]; however, no specific gene has been identified. Autosomal dominant inheritance is the proposed mechanism in such cases.[2] Some believe that the cysts originate from the neuroepithelium, but other sources, such as endoderm or ectopic respiratory tissue, have also been hypothesized. The cysts are thin-walled benign masses with a gelatinous content.[3] They are located in the anterior third ventricular area and are connected to the rostral aspect of its roof, projecting inferiorly close to the foramina of Monro.

The inner epithelium with simple cuboidal and columnar cells secretes a mucinous content, which accumulates under pressure. Most cysts are asymptomatic and rarely are a cause of headache. In symptomatic cysts, headache is the most common presentation. Persistent or intermittent obstruction of the foramina of Monro is believed to be the cause of headache.[4] Symptomatic cysts typically present in mid-adulthood with headache, signs of increased intracranial pressure, and acute lateral ventricular hydrocephalus, although atypical presentations (eg hemorrhagic cysts) have been described during childhood as well.[3]

Other symptoms may include altered mental status, nausea and vomiting, seizure, vertigo, and sudden attacks of leg weakness.[2] The latter might be rarely associated with other brain tumors and may be due to stretching of corticospinal nerve fibers to the legs after acute hydrocephalus. Cortical blindness due to bilateral occipital lobe infarction from posterior cerebral artery compression has been reported. The most severe presentation is sudden death. The cause of this rare phenomenon is debatable, but it may be secondary to reflex cardiac effects due to the cyst compressing of the hypothalamus.[2] Acute blockage of cerebrospinal fluid with instant herniation or decompensation in chronic hydrocephalus has also been postulated.[5]

The differential diagnosis of colloid cyst includes a wide range of tumors of the anterior third ventricle. These lesions usually originate outside the third ventricle and deform the ventricle by encroachment of the surrounding parenchyma; however, intraventricular tumors may also be the source of cerebrospinal fluid pathway blockage. Choroid plexus papillomas usually present during the first 2 decades of life. Although 10%-30% are found within the third ventricle, mobile tumors may slip from lateral ventricles into the foramina of Monro and become trapped in the third ventricle, thereby causing hydrocephalus.[6] Neurocytomas are intraventricular tumors that are seen in young adults and may be found in the lateral and third ventricular regions. These tumors are frequently misdiagnosed as oligodendroglioma or ependymoma under light microscopy, and the true incidence of this condition may be more than expected.


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