Diagnosis: idiopathic intracranial hypertension (pseudotumor cerebri)
This young female patient presents with a history typical for IIH: intermittent severe headaches with transient visual obscurations and visual loss. Another historical feature to ask about is pulse synchronous tinnitus (pulsatile tinnitus), which is present even more commonly than vision loss and is much more specific for the disease. This patient’s opening pressure was found to be 42, closing pressure 20 with marked improvement of symptoms.1
Optic nerve sonography can be used to identify intracranial hypertension through the measurement of the optic nerve sheath diameter (ONSD), since an increased intracranial pressure (ICP) of different etiologies results in enlargement of the ONSD.2,3,4
Take home points:
- To perform this scan, the conjuctiva should be protected from transmissible disease by either placing a large tegaderm over a closed eyelid (jelly on probe), or placing a tegaderm on the linear probe (sterile jelly on closed eyelid).5
- Both ONSDs should be measured 3 mm behind the papilla, an average of less than 5 mm is considered normal.2
- ONSD > 5 mm has been shown to be 90% sensitive and 85% specific for ICP > 20.6
- The optic nerve can be tricky to identify, so having the patient look slowly from one side to the other while scanning the orbit in different planes can aid in visualization.5
- The most accurate measurement of the ONSD will be when the ONS walls are parallel. Nonparallel walls can result in the false elevation of the ONSD.5
1. Wall M. Idiopathic intracranial hypertension. Neurol Clin. 2010;28(3):593-617. [PDF]
2. Blaivas M, Theodoro D, Sierzenski PR. Elevated intracranial pressure detected by bedside emergency ultrasonography of the optic nerve sheath. Acad Emerg Med. 2003;10(4):376-81. [PDF]
3. Moretti R, Pizzi B, Cassini F, Vivaldi N. Reliability of optic nerve ultrasound for the evaluation of patients with spontaneous intracranial hemorrhage. Neurocrit Care. 2009;11(3):406-10. [pubmed]
4. Geeraerts T, Merceron S, Benhamou D, et al. Noninvasive assessment of intracranial pressure using ocular sonography in neurocritical care patients. Intensive Care Med 2008;12(Suppl 2):117. [pubmed]
5. Dawson, Mallin. Introduction to Bedside Ultrasound, Volume 2. 2013. Apple iBook. [iBook]
6. Dubourg J, Javouhey E, Geeraerts T, Messerer M, Kassai B. Ultrasonography of optic nerve sheath diameter for detection of raised intracranial pressure: a systematic review and meta-analysis. Intensive Care Med. 2011;37(7):1059-68. [pubmed]
