Spontaneous Intracranial Hypotension: Atypical Radiologic Appearances, Imaging Mimickers, and Clinical Look-Alikes

“Acquired” Chiari malformation showing findings of CSF hypotension. A, Sagittal T1WI demonstrates a normal appearance of the posterior fossa of a 6-year-old patient with a ventriculoperitoneal shunt. B, Six years later, imaging demonstrates findings of overshunting resulting in CSF hypotension. This has previously (mistakenly) been called “acquired Chiari malformation.” In addition to descent of the tonsils, there is also effacement of the subarachnoid spaces, flattening of the pons, descent of the brain stem, and a decrease in the volume of the lateral and fourth ventricles, all of which indicate reduced CSF volume.

Bilateral subdural hematomas as an initial presentation in SIH. A, Sagittal T1WI shows a subtle decrease in the mamillopontine distance (white arrow). Otherwise, the typical stigmata of SIH are not present. B, Coronal postcontrast T1WI demonstrates large bilateral subdural hematomas with mass effect on the cerebral hemispheres. A hyperdynamic CT myelogram showed a leak in the thoracic spine, and a targeted blood patch was performed. The subdural hematomas subsequently required evacuation due to cerebral compression. All of the patient’s symptoms resolved, and the hematomas did not recur.

IgG4-related pachymeningitis. A, Coronal contrast-enhanced T1WI from a 53-year-old man with IgG4-related disease with Castleman-like features shows abnormal pachymeningeal enhancement (arrows). B, Follow-up imaging after steroid and rituximab (Rituxan) treatment demonstrates interval near resolution of the pachymeningeal enhancement.

Autonomic failure presenting as orthostatic headache. Beat-to-beat blood pressure (black) and heart rate (green) of an 80-year-old woman during a tilt-table test show a sustained drop in blood pressure during head-up tilt (gray shading). The lack of heart rate acceleration suggests neurogenic orthostatic hypotension. When her mean blood pressure fell below 85 mm Hg, she developed posterior head and neck tightness (coat hanger pain) and lightheadedness. Thus, pure autonomic failure was initially misdiagnosed as orthostatic headache.

SIH presenting with venous sinus thrombosis. A 43-year-old man presented with sudden onset of headaches, dizziness, and nausea clinically suspected to represent migraines. A, Contrast-enhanced T1-weighted image demonstrates diffuse, smooth, nonspecific thin pachymeningeal enhancement (arrows). The patient presented to the emergency department 3 days later with a marked increase in his headache and sudden onset of right lower-extremity weakness. D, Unenhanced coronal head CT demonstrates high attenuation and expansile content within the superior sagittal sinus and adjacent cortical veins, compatible with acute dural venous sinus and cortical vein thrombosis (selected clot highlighted by arrows). Sagittal MIP (B) and coronal (E) images from a contrast-enhanced CT venogram confirm a long-segment acute, expansile thrombus as a filling defect within the superior sagittal sinus, as well as multiple bilateral left-greater-than-right superior cortical veins (arrows). While he was being treated for sinus thrombosis, he reported that his headaches were orthostatic in nature. His condition continued to deteriorate with progression of the thrombosis despite treatment and parenchymal hemorrhage. Axial (C) and sagittal (F) T2WI demonstrates a ventral extradural fluid collection. A hyperdynamic CT myelogram was performed, and a leak was found at a spiculated osteophyte at T1-2.

SIH presenting as pituitary apoplexy. Sagittal T1WI (A) and coronal postcontrast T1WI (B) images demonstrate a hyperintense lesion filling the sella and extending into the suprasellar cistern. The patient was diagnosed with pituitary apoplexy of a macroadenoma or a Rathke cleft cyst and a Chiari I malformation. However, the MR imaging actually demonstrates the expected intracranial stigmata of an SIH, including severe brain sag and dural enhancement. Despite extensive evaluation, the source of the leak was not found. The patient was treated with a nontargeted blood patch. His headaches and imaging findings (C and D) resolved.