Submitted by Paulo Serapio, MD and Thomas Learch, MD.
History of Present Illness
45 year old male with no significant past medical history presents to an Urgent Care Clinic with a 3-4 month history of generalized headache acutely worsening over the past week, now an 8/10 in severity. This is associated with progressively worsening blurry vision bilaterally and generalized “fogginess”. He denies nausea or vomiting. He otherwise has no focal neurologic deficits. Recent workup at an outside hospital was unremarkable, notable for no imaging studies at the time.
Non-contrast CT brain was ordered from urgent care:
CT brain demonstrates a rounded, well demarcated 8mm hyperdense lesion at the foramen of monro with associated hydrocephalus. Periventricular hypodensity suggests transependymal edema. Generalized cerebral edema is also noted. No evidence for herniation. These findings are most consistent with acolloid cyst resulting in acute obstructive hydrocephalus.
The ordering MD was notified and the patient was transferred to the emergency department. He was seen by neurosurgery who planned for resection of the colloid cyst and placement of an extraventricular drain.
Pre-operative MRI demonstrates a slightly T1 hyperintense, T2 isointense lesion without significant contrast enhancement, consistent with a colloid cyst.
Post-operative imaging (Image 9) reveals interval placement of an EVD with decompression of the previously noted hydrocephalus. There is right frontal pneumocephalus and a small amount of air within the ventricles, consistent with postoperative changes. Subsequent CT brain performed 4 days postoperatively (Image 10) demonstrates resolving postoperative changes. A small amount of postoperative blood was seen at the foramen of monro (not pictured).
Colloid cysts are a benign, mucin containing cyst, most commonly found on noncontrast enhanced CT at the foramen of monro as a rounded, hyperdense mass of variable size. Roughly half of these cysts are discovered incidentally. The most common symptomatic presentation is headache with less commonly reported symptoms of visual disturbance, memory loss, nausea, and vomiting. Although histologically benign, clinical importance of these cysts is centered around the risk of causing an acute obstructive hydrocephalus which can rapidly progress to acute decompensation, herniation and death. As such, many asymptomatic colloid cysts without evidence for obstruction are also treated with complete surgical resection.
The differential diagnosis is relatively narrow when taking into account the combined CT and MRI appearance. Other masses that present in this region (e.g. subependymal giant cell astrocytoma) have contrast enhancement and less commonly present as a well demarcated, rounded mass when compared to colloid cysts. CSF flow artifact on MRI can mimic a colloid cyst, however, multiplanar MR imaging or NECT can help to distinguish the two.