A 9-year old girl is brought to the emergency department by her parents due to severe headache, lethargy, and vomiting. Her symptoms began a few weeks ago with mild intermittent headaches and fatigue and have progressively worsened. A CT scan of the brain reveals a mass lesion, enlarged lateral and third ventricles, and a normal-sized fourth ventricle. Which of the following is the most likely site of obstruction in this patient?

Question

A 9-year old girl is brought to the emergency department by her parents due to severe headache, lethargy, and vomiting.  Her symptoms began a few weeks ago with mild intermittent headaches and fatigue and have progressively worsened.  A CT scan of the brain reveals a mass lesion, enlarged lateral and third ventricles, and a normal-sized fourth ventricle.  Which of the following is the most likely site of obstruction in this patient?

Quizplus · Accepted Answer

11ec160b_35b2_e32a_9249_0b5a7e5fd21c_MD0001_00 Cerebrospinal fluid (CSF) is formed by 4 choroid plexuses found in each of the ventricles. The choroid plexus is composed of ependymal cell-covered outgrowths of pia mater capillaries that are fenestrated unlike other central nervous system (CNS) capillaries. The ependymal layer is a simple ciliated columnar epithelium with tight junctions between the cells. This selectively allows only certain materials from the blood to enter the CSF. Once formed, CSF flows from the lateral ventricles to the third ventricle via the interventricular foramina of Monro. It then circulates to the fourth ventricle through the cerebral aqueduct (of Sylvius). CSF then exits the fourth ventricle and enters the subarachnoid space via one of 3 foramina: the 2 lateral foramina of Luschka and the single midline foramen of Magendie. CSF is returned to the venous circulation via the arachnoid villi (granulations). This patient has findings consistent with noncommunicating (obstructive) hydrocephalus. Obstruction of CSF flow is most commonly caused by tumors, scarring (post-hemorrhage, infection), and CNS malformations. In this patient, obstruction at the level of the cerebral aqueduct causes increased pressures and ventricular dilation proximal to the site of blockage, which includes the lateral and third ventricles. The fourth ventricle is normal-sized as it is distal to the obstruction. In contrast, obstruction at the foramen of Magendie and Luschka would cause enlargement of all 4 ventricles (Choices D and E), while obstruction at the foramen of Monro would cause enlargement of only the affected lateral ventricle (Choice C). Other forms of hydrocephalus are described below: Communicating hydrocephalus presents with global ventricular dilation and increased intracranial pressure (ICP) without significant blockage to CSF flow within the brain or brainstem. It usually results from impaired CSF absorption by the arachnoid villi due to inflammation and fibrosis caused by hemorrhage or infection (Choice A). It rarely occurs due to increased production of CSF caused by papillomas of the choroid plexus. Normal pressure hydrocephalus presents with enlarged ventricles in the setting of normal ICP. It is considered to be a form of communicating hydrocephalus where impaired absorption of CSF is compensated for by decreased CSF formation. Although ICP is normal, there is still a pressure gradient between the ventricles and subarachnoid space which is responsible for the ventricular enlargement. Communicating hydrocephalus is more often found in infants and children, while normal pressure hydrocephalus is most commonly found in adults. Hydrocephalus ex vacuo presents with normal ICP and increased dilatation of ventricles secondary to cortical atrophy. It occurs most often in elderly patients with dementia. Pseudotumor cerebri presents with elevated ICP and classically occurs in young women who are overweight. The etiology of the condition is not well known, but it is thought to be related to cerebral venous outflow abnormalities due to elevated intracranial pressures. Educational objective: CSF flows from the third ventricle to the fourth ventricle via the cerebral aqueduct of Sylvius. Obstruction at this level can cause dilated lateral and third ventricles with a normal-sized fourth ventricle. Obstruction at the foramen of Monro would cause enlargement of only the affected lateral ventricle, while obstruction at the foramen of Magendie and Luschka causes enlargement of all 4 ventricles.

A 9-Year Old Girl Is Brought to the Emergency Department