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

Abstract

Spontaneous intracranial hypotension is a condition characterized by low CSF volume secondary to leakage through a dural defect with no identifiable cause. Patients classically present with orthostatic headaches, but this symptom is not specific to spontaneous intracranial hypotension, and initial misdiagnosis is common. The most prominent features of spontaneous intracranial hypotension on intracranial MR imaging include "brain sag" and diffuse pachymeningeal enhancement, but these characteristics can be seen in several other conditions. Understanding the clinical and imaging features of spontaneous intracranial hypotension and its mimickers will lead to more prompt and accurate diagnoses. Here we discuss conditions that mimic the radiologic and clinical presentation of spontaneous intracranial hypotension as well as other disorders that CSF leaks can imitate.

Fig 1.

Chiari type I malformation versus SIH. A, Sagittal T1WI demonstrates a Chiari type I malformation with descent of cerebellar tonsils 1.4 cm below the foramen magnum (black arrow). Note the typical “peglike” morphology. The prepontine cistern is preserved, and the pons maintains a rounded ventral morphology (white arrow). B, Sagittal T1WI in a patient with severe brain sag due to SIH shows mild descent of the cerebellar tonsils at the foramen magnum (black arrow), but with normal morphology. The pons is flattened (white arrow) with effacement of the prepontine cistern. There is also profound effacement of the subarachnoid spaces in the posterior fossa.

Fig 2.

“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.

Fig 3.

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.

Fig 4.

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.

Fig 5.

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.

Fig 6.

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.

Fig 7.

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.

Fig 8.

SIH presenting as superficial siderosis. A 37-year-old man who presented with episodes of dizziness and loss of consciousness was found to have diffuse posterior fossa–predominant superficial siderosis on axial SWI (A and B). Subsequent imaging of the spine demonstrated a ventral extradural fluid collection (curved arrow, C; straight arrows, D). A subsequent hyperdynamic CT myelogram identified the source of the CSF leak, which was surgically repaired.