Cranial venous outflow insufficiency; rendered almost invisible to radiological imaging by circular reasoning. Rethinking normal craniocervical venous anatomy.

Background And Purpose: Cranial venous outflow insufficiency, a model of brain dysfunction based on partial or intermittent obstruction to cranial venous drainage, is an attempt to explain a clinical phenotype characterised by multiple complex symptoms, including headache, fatigue and cognitive dysfunction, that can be responsible for long term neurological disability. This concept, however, has been received with some scepticism first, because its supposed symptoms seem mainly non-organic and, secondly, because its supposed lesions can be regarded as no more than variants of normal craniocervical venous anatomy. This reasoning, however, fails to appreciate that an understanding of normal venous anatomy has evolved, not from dedicated studies in healthy volunteers, but almost entirely from patients whose symptoms are assumed to be non-organic, or at least not referrable to the specifics of craniocervical venous anatomy. So, the reasoning is circular, and whilst this may not matter when frank venous thrombosis makes the diagnosis of venous disease clear, it might be frustrating attempts to understand the clinical expression of more subtle forms of cranial venous outflow compromise. Reassurance on this point, however, is only possible if it is inconceivable that the symptoms described by these patients could ever be referred back to the venous system, an assumption that has not been tested. The purpose of this study was to test this assumption by examining the clinical profile of patients who, by default, make a significant contribution to perceptions of normal venous anatomy, that is patients with MRI brain scans reported to be normal.

Method: Cross-sectional: we recorded the symptoms and diagnoses in 100 consecutive patients with MRI brain scans reported as normal.

Results: 26 % complained of headache, 25 % of focal neurological symptoms, 15 % of dizziness. 13 % had seizure/collapse. 46 % of patients had no final diagnosis. 18 % were diagnosed with migraine, 7 % with functional neurological disorder and 6 % with epilepsy.

Conclusions: The clinical overlap between patients with brain MRI reported as normal and patients with known venous sinus disease, as documented in the literature, raises strong concerns regarding their role in defining normal craniocervical venous anatomy. Current assumptions regarding this anatomy, therefore, are probably unsafe, this inviting a re-evaluation of the clinicopathological significance of hitherto almost ignored configurations of cranial venous outflow, such as jugular venous narrowing or outflow asymmetry, and giving encouragement to explore a pathological substrate in cranial venous outflow insufficiency for a range of otherwise unexplained symptoms.