There is no direct relationship between PI response and smooth muscle contraction of rat trachea stimulated by alpha-agonists.

To the Editor: We read with interest the case report “Postpartum postural headache due to superior sagittal sinus thrombosis mistaken for spontaneous intracranial hypotension” by Chilsholm and Campbell.1 In that report a patient was eventually diagnosed with a sagittal sinus thrombosis after undergoing a lumbar epidural blood patch (LEBP). Of note, the patient had a magnetic resonance imaging (MRI) of the brain prior to the LEBP reported as normal aside from evidence of venous congestion. MRI is emerging as a useful tool for recognizing intracranial hypotension (IH). MRI studies of patients with IH commonly show on post-contrast image abnormal, intense, diffuse, symmetric, contiguous dural-meningeal (pachymeningeal) enhancement.2 This enhancement usually involves much of the supratentorial and infratentorial intracranial dural mater, including the convexities, interhemispheric fissure, tentorium, and fax cerebri. Abnormal leptomeningeal enhancement is usually absent except in more acute states, when abnormal enhancement of the dural venous sinuses may be noted.2 It is unclear in the report if the initial MRI was performed with gadolinium contrast. If this was the case, it would have been unusual to pursue a diagnosis of IH with a MRI showing venous congestion with no post-contrast pachymeningeal enhancement. This would have alerted the clinician about the unlikely diagnosis of IH for the etiology of the patient’s headache and avoided her an unnecessary lumbar epidural blood patch.