Occlusion of the major dural venous sinuses (superior longitudinal and lateral) results in increased ICP. This is not surprising in view of the direct effect of venous obstruction on CSF pressure. One such form, caused by lateral sinus thrombosis, was referred to by Symonds as “otitic hydrocephalus,” a name that he later conceded was inaccurate insofar as the ventricles are not enlarged in this circumstance. Venous congestion that complicates heart failure and superior mediastinal obstruction also raise the CSF pressure, again without enlargement of the ventricles. This may happen as well with large, high-flow arteriovenous malformations of the brain. The effects of cerebral venous occlusion are considered further in the discussion of pseudotumor cerebri (below) and in Chap. 33 in the context of thrombosis of the cerebral venous sinuses. The role of compression of the large venous channels in cases of raised ICP from a mass has not been fully explored, but it may explain some of the intractable aspects of these cases.
This term was coined by Nonne in 1914 and has remained a useful means of designating a syndrome of headache, papilledema (unilateral or bilateral), minimal or absent focal neurologic signs, and normal CSF composition, all occurring in the absence of enlarged ventricles, or an intracranial mass on CT scanning, or MRI. Being a syndrome and not a disease, pseudotumor cerebri has a number of causes or pathogenetic associations. However, the most common form of the syndrome has no firmly established cause, that is, it is idiopathic and is generally referred to as idiopathic intracranial hypertension.
This syndrome was described in 1897 by Quincke, who called it “serous meningitis.” It is particularly frequent in overweight adolescent girls and young women, attaining an incidence of 19 to 21 per 100,000 in this group, as compared with 1 to 2 per 100,000 in the general population (Radhakrishnan et al). The features of increased ICP develop over a period of weeks or months. Relatively unremitting but fluctuating headache, described as dull or a feeling of pressure, is the cardinal symptom; it can be mainly occipital, generalized, or somewhat asymmetrical. Other, less-frequent complaints are blurred vision, a vague dizziness, minimal horizontal diplopia, transient visual obscurations that often coincide with the peak intensity of the headache, shoulder and neck pains, or a trifling numbness of the face on one side. Rarely, the presenting feature may be a nasal CSF leak, as pointed out by Clarke and colleagues. Self-audible bruits have been reported by some patients; this has been attributed to turbulence created by differences in pressure between the cranial and jugular veins.
The patient is then discovered to have flagrant papilledema, raising the specter of a brain tumor. Rarely, papilledema is only minimally developed or absent or, conversely, papilledema alone, without headache, is the only manifestation of the disease. The risk of visual loss, and the severity of headache make the formerly used term benign intracranial hypertension less appropriate.
The CSF pressure is found to be elevated by lumbar puncture, usually in the range of 250 to 450 mm H2O, but it is not clear whether the brain itself is swollen or, as is more likely, the increased pressure is the result of a change in the pressure within the CSF and venous compartments. When the CSF pressure is monitored for many hours, there are fluctuations taking the form of irregularly occurring plateau waves of increased pressure lasting 20 to 30 min, and then falling abruptly near to normal (Johnston and Paterson).