Ultrasound

Idiopathic Intracranial Hypertension

THE CASE

A 22 year-old female with a medical history of migraines and obesity who presents to the Emergency Department with a headache. Her headache was gradual in onset, but has progressively worsened and has not been relieved with NSAIDs. She describes the headache as dull and pounding with photophobia and phonophobia. She also notes associated nausea but no vomiting, and no associated neurologic complaints. She does note that she thinks during a previous ED visit at an outside hospital she was told she may have “high pressure in her head” but she does not remember the details and is not on any medication for it. A bedside ocular ultrasound was performed and the following images were obtained:

Figure 1. Transverse view of right eye

Figure 1. Transverse view of right eye

Figure 2. Transverse view of left eye

Figure 2. Transverse view of left eye

DIAGNOSIS

An LP was performed and the opening pressure was mildly elevated at 33 cm H2O that decreased to 18 cm H2O with removal of 20 cc of fluid. The remainder of labs and imaging were normal. The patient was diagnosed with Idiopathic Intracranial Hypertension and started on Diamox with outpatient neurology and ophthalmology follow-up. On follow-up she reports resolution of headaches.

DISCUSSION

The ultrasound images were obtained using the 7.5 MHz high frequency linear probe. The ophthalmic setting was used given its lower thermal index, thus decreasing the risk of injury to the eye from heat exposure. For patient comfort, a non-adhesive sterile dressing was placed over eye prior to application of a copious amount of ultrasound gel. The ultrasound probe was placed lightly over the gel in a transverse orientation with probe marker to the patient’s right and with careful attention not to exert pressure on the globe. The probe was angled superiorly and inferiorly slowly until the optic nerve came into view as a black stripe extending posteriorly from the rear of the globe. The nerve sheath diameter was then measured 3 mm posterior to the optic disc. For a more accurate value, an average of 2-3 measurements can be taken.

The relationship between intracranial pressure and optic nerve sheath diameter has been well established. In general, an optic nerve sheath diameter of >5.0 mm is considered abnormal, however there remains some controversy about the exact diameter of the optic nerve sheath that best predicts elevated intracranial pressure. For example, one prospective blinded observational study by Kimberly et al. in 2008 found that an optic nerve sheath diameter >5.0 mm correlated with an elevated intracranial pressure with a sensitivity of 100% and a specificity of 63%. Another 2013 study by Amini et al measured the optic nerve sheath diameter of 50 atraumatic patients undergoing lumbar puncture and found that an optic nerve sheath diameter greater then 5.5 mm correlated with an elevated ICP (>30 mm Hg) with a sensitivity and specificity of 100%. Finally, a third study by Qayyum found a sensitivity of 100% and specificity of 75% for a cutoff of 5.0 mm.

In general, measurement of optic nerve sheath diameter appears to be a useful adjunct for detection of elevated intracranial pressure due to the fact that it is non-invasive, easily performed at bedside, and has good sensitivity for detecting increased intracranial pressure. Though a normal optic nerve sheath diameter does not exclude a life-threatening intracranial process, an elevated optic nerve sheath diameter can further support a diagnosis of elevated intracranial pressure when in the right clinical context.

Faculty Reviewer: Dr. Kristin Dwyer

Additional resources

  1. Blaivas, M. , Theodoro, D. and Sierzenski, P. R. (2003), Elevated Intracranial Pressure Detected by Bedside Emergency Ultrasonography of the Optic Nerve Sheath. Academic Emergency Medicine, 10: 376-381.

  2. 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 Jul;37(7):1059-68.

  3. Irazuzta JE, Brown ME, Akhtar J. Bedside Optic Nerve Sheath Diameter Assessment in the Identification of Increased Intracranial Pressure in Suspected Idiopathic Intracranial Hypertension. Pediatr Neurol. 2015 Aug 28.

  4. Qayyum H, Ramlakhan S. Can ocular ultrasound predict intracranial hypertension? A pilot diagnostic accuracy evaluation in a UK emergency department. Eur J Emerg Med. 2013;20(2):91–97.

  5. Shevlin C. Optic Nerve Sheath Ultrasound for the Bedside Diagnosis of Intracranial Hypertension: Pitfalls and Potential. Critical Care Horizons 2015; 1: 22-30.

  6. Tayal VS, Neulander M, Norton HJ, et al. Emergency department sonographic measurement of optic nerve sheath diameter to detect findings of increased intracranial pressure in adult head injury patients. Ann Emerg Med. 2007 Apr;49(4):508-514.

Take My Breath Away

Case Presentation

A 31 year old female with no significant PMH presents to the Emergency Department with left-sided chest pain that started suddenly 3 hours ago while sitting in a lecture hall.  She describes the pain as a constant stabbing sensation in her left anterior chest that radiates to her left neck.  She endorses feeling short of breath and lightheaded.  She has never had a sensation like this before.  The patient denies smoking, fevers, chills, and trauma.  Her vital signs are unremarkable, and her physical exam is notable for decreased breath sounds in the left upper lung field. 

 

Ultrasound Exam

Left Anterior.jpg


The above images are of the left anterior chest and were acquired using the linear probe.  The curvilinear probe may also be used for lung ultrasound.

Diagnosis:  Left spontaneous pneumothorax (PTX)

 

What do we see in these images?

In the video, we see a pleural line that is static without the classic “sliding.”  In an ultrasound of a healthy normal lung, we should see a to-and-fro movement or shimmering of the pleural line. This has often been described as ants on a log. In the case of pneumothorax, however, there is air between the visceral and parietal pleura that prevents visualizing of the visceral pleura and inhibits lung sliding. 

In the still image of M-mode, we see a pattern of horizontal lines above and below the pleura.  This pattern is referred to “barcode” sign, and is indicative of a lack of movement.

 

Is U/S good at detecting pneumothorax?

Sensitivity Specificity
U/S 78.6 98.4
CXR 39.8 99.3


Ultrasound is both a quick and reliable tool for the diagnosis of pneumothorax.  In fact, ultrasound is more accurate than chest radiography at detecting PTX in the supine patient.

 

Faculty Reviewer: Dr. Kristin Dwyer 

References:

  1. Alrajab S, Youssef AM, Akkus NI, Caldito G. Pleural ultrasonography versus chest radiography for the diagnosis of pneumothorax: review of the literature and meta-analysis. Critical Care. 2013;17(5):R208. doi:10.1186/cc13016.

  2. Husain LF, Hagopian L, Wayman D, Baker WE, Carmody KA. Sonographic diagnosis of pneumothorax. Journal of Emergencies, Trauma, and Shock. 2012;5(1):76-81. doi:10.4103/0974-2700.93116.

Ultrasound Case of the Month: A Silent Killer

The Case:

A 72 year old male with no PMH presents to the emergency department (ED) for vague abdominal discomfort and fullness. The patient is hemodynamically stable on arrival and received a point of care ultrasound (POCUS) for evaluation of his abdominal pain. FAST performed was negative for free fluid, however, the renal ultrasound showed unilateral mild hydronephrosis on the right side. POCUS was then performed to evaluate the aorta, and a large abdominal aortic aneurysm (AAA) was seen, measuring 14cm at its largest diameter.

 

Introduction:

When performing a POCUS it is important to remember the differential diagnosis for hydronephrosis is broad, and not limited to renal colic. The ureter can be obstructed either internally from a stone, or externally from surrounding structures.  When renal colic is on your differential, and you find hydronephrosis, be sure to also consider alternative diagnosis such as a AAA. In older patients, consider performing a AAA evaluation in all patients with suspected renal colic, and/or hydronephrosis. 

In this case, the patient had compression of the ureter from the large AAA resulting in hydronephrosis, but if the aorta had not been evaluated, we may have missed the more dangerous diagnosis. In addition, please remember that a patient may have leaking or rupture from the AAA which is located retroperitoneally and may not be seen on POCUS.

A ruptured abdominal aortic aneurysm (AAA) is a vascular catastrophe responsible for 1-3% of deaths in men from the age 65-85 in developed countries. Rupture from an AAA is the 10th leading cause of death in males over 50, the mortality rate of a ruptured AAA approaches 90% and the incidence of AAA continues to increase. Therefore, it is essential for the EM physician to diagnose a AAA in a timely manner. (1) The minority of patients with a ruptured AAA (<25%) will present with the classic triad of hypotension, back pain and a pulsatile abdominal mass.  This results in a delay in diagnosis, or misdiagnosis. Patients may present with referred pain to the scrotum, buttocks, thighs, shoulders, and/or chest and can be misdiagnosed as having renal colic, diverticulitis or MSK pain.

Indications:

The current indications by ACEP for obtaining POCUS to detect AAA include:

Presence of syncope, shock, hypotension, abdominal pain, abdominal mass, flank pain or back pain- especially in patients >50 years old.(3) Currently, the U.S. Preventive Service Task Force recommends that men from the age of 65-75 years who have ever smoked be screened for an AAA sonography.(4)

Utility of bedside ultrasound for AAA in the ED?

While CTA is considered the surveillance study of choice(5),  research suggests that the sensitivity of point of care bedside ultrasound approaches 99% for abdominal aortic aneurysm (AAA). With such a excellent sensitivity and a high prevalence of AAA in specific patient populations (10-15% in men who smoke >65), providers should consider performing this scan at the bedside for an expedited diagnosis.(6)

Performing the scan:

  • The probe of choice is the 3.5 MHz curvilinear probe

  • Start just caudal to xyphoid process

  • Measure the aorta proximally, mid and distally in the transverse plane with the probe marker to the patient’s right (should be <3cm from outer to outer wall)

  • Measure the iliac arteries after the bifurcation in transverse (should be <1.5cm)

  • Evaluate the aorta distally in the longitudinal view with the probe marker to patient’s head as most aneurysms will be located infrarenally

  • Identify vertebral body as relevant landmark

  • Aorta is anterior to vertebral body

  • IVC is anterior & right (patient’s right) of vertebral body

Vertebral body: horseshoe shaped with hyperechoic anterior &amp; posterior shadowing

Vertebral body: horseshoe shaped with hyperechoic anterior & posterior shadowing

Tips and Tricks

  • Aorta and IVC can be confused in longitudinal view:

    • Aorta is rounder, less compressible, & has brighter thicker walls

  • Bowel gas & body habitus can make imaging difficult:

    • Apply steady pressure to move gas

    • Jiggle the probe to move bowel aside

    • Flex patients hips & knees to relax abdominal muscles

    • Lower probe frequency to improve sound wave penetration

Conclusion

POCUS scanning for AAA enables timely diagnosis of a condition with high mortality which is frequently misdiagnosed, or suffers a delay in diagnosis. AAA POCUS has high sensitivity and specificity that can be easily learned and performed in ED. In a patient with hydronephrosis, consider also AAA evaluation, even if renal colic is high on your differential diagnosis.

Faculty Reviewer: Dr. Kristin Dwyer

References:

  1. Sakalihasan N, Limet R, Defawe OD. Abdominal Aortic Aneurysm. Lancet 2005;365:15577-89.

  2. Fink HA, Lederle FA, Roth CS, Bowels CA, Nelson DB, Haa MA. The Accuracy of physical examination to detect abdominal aortic aneurysm. Arch Intern Med.2000;160(6):833-6.

  3. American College of Emergency Physicians. Policy Statement. 2001: Emergency Ultrasound Guidelines.

  4. U.S. Preventive Services Task Force. Screening for abdominal aortic aneurysm: recommendation statement. Ann Inter med. 2005;142(3):198-202.

  5. Cantisani V, Ricci P, Grazhdani H, et al. Prospective comparative analysis of colour-doppler ultrasound, contrast-enhanced ultrasound, computed tomography and magnetic resonance in detection endoleak after endovascular abdominal aortic aneurysm repair. Eur J Vasc Endovasc Surg. 2011;41:(2)186-92.

  6. Rubano, Elizabeth, Ninfa Mehta, William Caputo, Lorenzo Paladino, and Richard Sinert. Systematic Review: Emergency Department Bedside Ultrasonography for Diagnostic suspected Abdominal Aortic Aneurysm. Acad Emerg Med Academic Emergency Medicine 20.2 (2013): 128-38.