The association between cranial venous outflow obstruction and PTS dates back to the earliest descriptions of the latter condition, indeed even prior to the reports of Quincke [138, 139] and Nonne  which are generally taken to represent the first recognition of a specific condition initially called either meningitis serosa (Quincke, 1893) or pseudotumor cerebri (Nonne, 1904). Thus Taylor wrote in the 1890 edition of The Practice of Medicine: ''It is important to remember what has now been verified in numerous cases that in mastoid suppuration there is often double optic neuritis with an entire absence of meningitis or abscesses proved by post-mortem examination, or by recovery after simple trephining of the mastoid cells.'' The link with ear disease was through involvement of the lateral sinuses by the disease itself, or through internal jugular vein ligation as a means of treatment. For example, Newton Pitt, also in 1890 , described three patients, all of whom had papilloedema but no other CNS signs, and who recovered, one having had a lateral sinus explored with clot removal, and the internal jugular vein ligated.
In the first three decades of the 20 th century there were numerous reports of PTS occurring in conjunction with chronic suppurative otitis media and mastoiditis to the extent that Symonds  in 1931 felt able to define a condition of otitic hydrocephalus in which CSF excess due to over-production or impaired absorption followed cranial venous sinus, particularly but not exclusively transverse sinus obstruction, occurring secondary to chronic middle ear or other infection. In addition, Liedler in 1928  was probably the first to describe PTS after ligation of one or both internal jugular veins in the treatment of chronic ear disease. Symonds' concept did not, however, survive the neuroradiological developments of the 1930s when the newly introduced techniques of encephalography and ventriculography showed that there was no demonstrable increase in the volume of fluid in the intracranial CSF-containing spaces in these cases. This has, of course, been an enduring difficulty in establishing a disturbance of CSF hydrodynamics as primary in PTS. Whatever the precise mechanism, the association of PTS with chronic ear disease and venous sinus pathology remained important. Thus in other significant reports from the 1930s, six of the fifteen cases reported by Davidoff & Dyke  had chronic suppurative otitis media or other infection whilst all of Gardner's  cases had chronic ear disease, the majority also having lateral sinus occlusion.
In parallel with the literature on so-called 'otitic hydrocephalus' a series of cases was published describing ''traumatic hydrocephalus'' . This misnomer was used to describe cases of PTS occurring after closed head injury, either with or without skull fractures. The association between closed head injury and venous sinus obstruction was first proposed by Ecker in 1946  but was not confirmed using venography until later by several other groups [11, 84, 109]. These cases were distinct from those in which there was a depressed fracture fragment or a penetrating injury. Most cases involved either a non-displaced linear occipital skull fracture crossing the sinus or a closed head injury without a fracture.
By the 1950s the relation between PTS and cranial venous sinus pathology, particularly secondary to chronic ear infection, was well-established, although hydrocephalus had been excluded. In an important paper in 1955, Foley  collected from the literature 46 cases of benign intracranial hypertension (a term which he introduced) which he labeled as otitic and described 60 cases of his own of which 13 were otitic or cerebral venous in origin. In 25 cases with right-sided otitis media mastoidectomy was performed in 21. Thrombosis of the lateral sinus was proven at surgery in 14 cases whilst another 6 had some type of sinus involvement such as perisinus abscess. Of the 13 cases with left-sided otitis media, mastoidectomy was performed in 9 with lateral sinus thrombosis in 3 and other involvement of the lateral sinus in 2 more. Five cases had bilateral ear disease and of these 4 went on to mastoidectomy. In 2 there was left-sided lateral sinus thrombosis and in 2 the sinuses were apparently normal. Foley proposed that lateral sinus thrombosis, presumably of the dominant sinus, rather than thrombosis of the superior sagittal sinus (SSS), was the primary pathology in otitic PTS.
Four other aspects of the possible link between PTS and cranial venous outflow obstruction were also documented by this time. First, Evans  gave further evidence of PTS following internal jugular vein ligation although in reviewing other reports as well as his own cases he found that none of the 7 patients having bilateral ligation for non-otitic problems developed papilloedema whereas the 3 cases who had the procedure in relation to ear disease did. Of 6 cases who had unilateral ligation for bilateral ear disease only one developed papilloedema. Second, there were several reports linking PTS with chronic respiratory disease and cardiac failure with the presumption of increased venous pressure [6, 21, 155]. Third, there were the first reports linking PTS with blood disorders which could be presumed in some instances to act through venous obstruction [38, 103, 172]. Fourth, and most significant, was the study by Ray and Dunbar  who used the technique of direct sinography in which a catheter was introduced via a burr-hole into the anterior segment of the SSS. They studied 4 patients, 2 of whom were identified as having PTS without any antecedent factors. Both had failed to respond satisfactorily to subtemporal decompression and both showed evidence of obstruction in the posterior segment of the SSS with elevation of intra-sinus pressure, one going on to clot removal with apparent benefit. A third case, described as a typical case of 'otitic hydrocephalus', was found to have complete obstruction of the right transverse sinus and a small left transverse sinus. There was measured elevation of SSS pressure [320 mmH2O]. Their remaining case would not qualify for the diagnosis of PTS. The authors recommended sinography be introduced for the investigation of patients with PTS. They also proposed that the formation of collaterals after venous sinus obstruction was the mechanism for the spontaneous resolution of symptoms. Foley  also performed venography on a wider population of patients with PTS. Sixty cases were reviewed; 11 of which were classified as otitic hydrocephalus. Angiography was performed in 13 cases, however, only the patency of the SSS drew direct comment.
In the period between 1960 and 1980 the connection between PTS and cranial venous outflow obstruction fell out of prominence for a number of reasons. Among these may be numbered the introduction of effective antibiotic treatment which sharply reduced the incidence of chronic middle ear infection, the considerable number of other putative aetiological factors in
PTS which would not be thought to act through venous sinus obstruction, and the introduction of CT scanning which reduced the likelihood of recognizing cranial venous outflow tract pathology. The report of Janny et al.  in 1981 might, however, be taken as signalling the return of focus on the role of cranial venous outflow in PTS, a focus which has sharpened over the last two decades with the technical advances referred to in the introduction. Their study, and those that have followed, will be considered in detail in what follows.
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