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Diagnosis Deconstructed

Diagnosis Deconstructed: Hernias and Tonsils

Morchi, Ravi MD

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doi: 10.1097/01.EEM.0000455725.45621.84
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    She was transferred to us with uncal herniation and papilledema. Awake and alert, she complained of a gradually worsening headache since delivery of a healthy infant a month earlier.

    She had blurred vision and nausea but no focal weakness or fever. She had a history of migraines, her heart rate was consistently in the 50s, and her blood pressure ranged from 100/50 to 130/80 mm Hg.

    Uncal herniation. With medial and inferior displacement of the uncus of the temporal lobe around the tentorium cerebelli, the first finding expected is pupil dilation from compression of the outer CN III. Worsening herniation may cause compression of the innermost CN III fibers; it also deviates the globe laterally and inferiorly. Pressure on the ipsilateral PCA can result in ischemia to the occipital lobe and contralateral homonymous hemianopsia. Downward force on the RAS impairs consciousness. The culprit mass may cause contralateral hemiparesis, but extensive uncal herniation can affect corticospinal fibers running on the contralateral side of the brainstem, producing the false-localizing sign of UMN weakness ipsilateral to the dilated pupil. Our patient was awake and had reactive pupils, no hemianopsia, and no hemiparesis. Her exam was not consistent with uncal herniation.

    Extraocular motion was intact, facial muscles were strong, pharynx and palate were normal, and motor function was 5/5. No pronator drift, clonus, or hyperreflexia.

    CT. The suprasellar and interpeduncular cisterns were open and symmetric. I did not see radiographic evidence of any type of herniation: uncal, subfalcine, or otherwise. No mass, IPH, or SAH. Sulci and gyri seemed effaced, however, and consistent with diffuse cerebral edema.

    Ultrasound. Our resident investigated the patient's papilledema. Bilateral optic nerve sheath diameters (ONSD) were 7-8 mm. CN II is actually part of the central nervous system, but unlike the other cranial nerves, it is encased by dura, arachnoid, and pia, and elevated ICP strangulates it circumferentially, rather than compressing it from one direction. The nerve becomes ischemic as pressure exceeds capillary perfusion. She has papilledema on exam and bilateral ONSDs consistent with elevated ICP threatening vision.

    Cerebral edema without hydrocephalus. CSF is making its way from the choroid plexus through the lateral and third ventricles and aqueduct into the fourth ventricle. It proceeds out the foramen of Magendie and Luschka into the subarachnoid space. It must be transferred across arachnoid granulations from the subarachnoid space into the dural sinuses. Insufficiency of granulations occurs in SAH and meningitis when blood products or inflammatory debris block them.

    Stenotic or insufficient dural sinuses are thought to play a role in idiopathic intracranial hypertension. Thrombosis of these sinuses. A noncontrast CT is not necessarily going to rule this out. Arrangements are made for an MRI and MRV.

    I wonder about arterial causes of diffuse edema. Are we missing something by only focusing post-brain? Ischemia disrupts electrical gradients, and cells swell. Could her neuronal edema be secondary to a diffuse arterial cause?

    (Pre)eclampsia is the most common dynamic vasculopathy of the peripartum period. She is already four weeks post-delivery, however, and her blood pressure peaked only at 130/80 mm Hg. She has no proteinuria or SQ edema, has not seized, or had a change in alertness.

    Posterior reversible encephalopathy syndrome classically involves the PCAs. Abnormal ONSDs in our particular case indicate visual dysfunction related to elevated ICP and CN II strangulation, not occipital lobe ischemia.

    Reversible cerebral vasoconstriction syndrome. Another type of vascular insufficiency that can cause headache and ischemia-induced edema. But without focal findings, this falls lower on our differential diagnosis.

    Cerebral arterial dissection. It would have to be extensive and bilateral to produce diffuse edema, elevated ICP, papilledema, or abnormal ONSDs.

    I concluded her problem must be on the venous end. Her MRV was read as “symmetric signal dropout in bilateral transverse sinuses.” The absent venous signal seemed awfully symmetric. Too symmetric to be pathologic. It was also confined to short segments of the transverse sinuses. Our neurosurgeon was similarly skeptical of thrombi in these locales. The superior and inferior sagittal sinuses had normal flow.

    But there was something else not appreciated on the thicker cuts of a noncontrast head CT. Her cerebellar tonsils were herniating through her foramen magnum. Compression of her cervicomedullary junction impaired CSF flow at Magendie, resulting in elevated ICP despite the superior Luschka foramen patency mitigating the appearance of hydrocephalus.

    This is a Chiari 1 malformation. She received CSF diversion through an external ventricular drain, and ICPs were documented in the 30s. An urgent suboccipital craniectomy, C1 laminectomy, and partial debulking cerebellar tonsillectomy were performed to relieve pressure on the brainstem and restore CSF flow around the cervicomedullary junction. Three percent NS siphoned off remaining neuronal edema post-operatively. She improved and was discharged.

    Her long history of migraines may simply have been recurrent craniocervical CSF obstruction because of the redundant cerebellar tonsils of a Chiari 1 malformation. Eventually, it became an emergency.

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