The Nutcracker

The anterior pararenal space is tight real estate.  Of the many vascular structures in this area, one vessel in particular has to make a reach over and through multiple other structures to reach its destination... the left renal vein.  The left renal vein also acts as the final common conduit for multiple other draining veins including the left gonadal vein, left adrenal vein, left lumbar veins, and left inferior phrenic vein... so narrowing at the downstream left renal vein can result in dilatation of these upstream veins formation of varices, and renal venous hypertension.

If a mass were compressing the renal vein at this point, then the etiology and the downstream effects are usually straightforward... but occasionally, if a patient's thorax has a narrow AP diameter, the left renal vein can be compressed between the superior mesenteric artery and the aorta, like a nutcracker.

Below is an example:

59 Y lady receiving an arterial runoff study for lower extremity disease, found to incidentally have dilatation of the left ovarian vein and venous congestion in the pelvis.

The patient below was receiving an MRA of the chest and abdomen to rule out an aortic aneurysm (which was not present), but likely due to her narrow AP diameter, there was asymptomatic compression of her left renal vein with more prominent dilatation of the left lumbar veins than the left gonadal vein.

38Y lady with a negative exam for evaluation of aortic aneurysm. Incidental compression of the left renal vein and dilatation of the left ovarian and left lumbar veins

Another opportunity for compression of the left renal vein occurs with the retroaortic left renal vein:

Although the "nutcracker" morphology may exist, it only becomes a "syndrome" if there are associated clinical symptoms such as flank pain, left-sided varicocele, hematuria, chronic fatigue, or even autonomic dysfunction.  Severely symptomatic left renal nutcracker phenomenon has been treated with transposition of the left renal vein (below)

The term "nutcracker syndrome" also refers to a similar situation in the retroperitoneum in which a narrow AP diameter results in the duodenum being crushed between the aorta and superior mesenteric artery, resulting in obstruction.

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1. Duty B, Daneshmand S. "Venous Resection in Urological Surgery." The Journal of Urology. 180:6, Dec 2008, pp 2338-2342.
2. Hohenfellner M, D'Elia G, Hampel C, et al. "Transposition of the Left Renal Vein for the Treatment of the Nutcracker Phenomenon: Long Term Follow-up" Urology. 59:3, March 2002, pp 354-357.
3. Rudloff U, Holmes RJ, Prem JT, et al. "Mesoaortic Compression of the Left Renal Vein (Nutcracker Syndrome): Case Reports and Review of the Literature" Annals of Vascular Surgery. 20:1, Jan 2006, pp 120-129.

Coronary Anomaly: Single Coronary Artery

The difference between a coronary artery variation and a coronary artery anomaly is somewhat subjective.  Although some coronary artery variations seem clearly to be disadvantageous (such as a "malignant course of the right coronary artery"), others are less clearly so.

Instead on differentiating variant from anomaly based on possible prognostics, some use the term as a measure of prevalence: anomalies are fewer than 1%... variations more than this.

One interesting and extremely rare anomaly that arises in 0.025 - 0.04% of patients is the single coronary artery.

The single coronary artery can arise from either the right or left cusp and continue with a coronary artery on the same side with a branch to the opposite side... or it can have a completely anomalous course. Like with the "malignant course" mentioned above, a patient is at increased risk for sudden death if the coronary crosses between the pulmonary artery and the aorta. A proximal stenosis in a single coronary artery is likewise a grave problem since obviously both vascular territories are at risk.

Single coronary artery in an 80Y man.  Oblique VR image of the top of the heart shows only one coronary artery arising from the left coronary sinus.  The RCA courses between the aorta and the pulmonary artery (Radiographics).

Single coronary artery in an 80Y man.  On a sagittal oblique VR image, the single coronary artery demonstrates a high takeoff above the sinotubular junction (Radiographics)

Single coronary artery in a 55Y man. Coronary angiogram shows the anomalous origin of the hypoplastic RCA which arises from the LAD and courses anteriorly to the pulmonary artery (Radiographics)

Some sources state that a single coronary artery is associated with other cardiac anomalies and a careful evaluation of the rest of the heart should be pursued.  A classification scheme has also been proposed, bascially dividing between a dominant single coronary artery that supplies the whole myocardium (group 1) and a single coronary artery ostium and single coronary artery trunk that bifurcates into the left and right side of circulation (group 2). Due to the small numbers of patients, there does not seem to be a consensus whether the single coronary artery occurs more frequently on the left or right, or whether a group 1 or group 2 anomalies is more common.

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1. Clinical Cardiac CT: Anatomy and Function. Halpern E. 2nd ed. 2011. Chapter 4.
2. Kim SY, Seo JB, Do KH, et al. "Coronary Artery Anomalies: Classification and ECG-gated Multi-Detector Row CT Findings with Angiographic Correlation." March 2006 Radiographics 26,317-333.
3.Sharbaugh AH, White RS. "Single Coronary Artery: Analysis of the Anatomic Variation, Clinical Importance, and Report of Five Cases.". JAMA 1974; 230(2):243-246.
4. Lipton MJ, Barry WH, Obrez I, et al. "Isolated Single Coronary Artery: Diagnosis, Angiographic Classification, and Clinical Significance" Radiology 130:39-47, Jan 1979

The Pulse Sometimes Strikes Twice

"Bis" + "feriens" = "twice strikes"

A waveform with two systolic phases is said to be pulsus bisferiens, and joins that small infamous group of Latin pulses, including alternans, and paradoxicus. So what causes pulsus bisferiens, and what causes the waveform?

It may be easier to think of it as a normal pulse with "mid systolic retraction" rather than a pulse with "two strikes"... pulsus vacuumus, if you will.  But despite the fact that pulsus bisferiens has been recognized for at least five hundred years, its mechanism is still not fully understood.

First, an example of a normal CCA waveform as a baseline:

Then, the pulsus bisferiens

The arrow points to the "mid systolic retraction." The wedge points to the normal dicrotic notch. The dicrotic notch is a normal finding and is due to closure of the aortic valve, temporary cessation of forward flow, followed by resumption of forward flow driven by elastic rebound of aortic wall.(1)

The three entities most closely with a pulsus bisferiens are aortic regurgitation, combined aortic regurgitation and aortic stenosis (with regurgitation dominant), and HOCM (hypertrophic obstructive cardiomyopathy).

Aortic regurgitation

Since carotid ultrasound is not usually performed simultaneously with ECG, the diagnosis can only be made with certainty when a dicrotic notch is clearly present.  Pulsus bisferiens may exist without a dicrotic notch visible on the spectral ultrasound waveform, but this finding is technically indeterminate.

Pulsus bisferiens is most often encountered on vascular ultrasound of the common carotid arteries, and may be the first finding of valvular disease... oddly enough it is palpated more effectively in the peripheral arteries.

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1. Rohen EM, Kliewer MA, Carroll BA, Hertzberg BS. "A Spectrum of Doppler Waveforms in the Carotid and Vertebral Arteries." AJR December 2003 vol. 181 no. 6 1695-1704
2.Kallman CE, Gosink BB, Gardner DJ. Carotid Duplex Sonography: Bisferious Pulse Contour in Patients with Aortic Valvular Disease." AJR August 1991 vol. 157 no. 2 403-407

Crouching Bunny, Hidden Stenosis

Carrying on with the innominate artery theme, Zweibel notes in his textbook that a biphasic (or "crouching bunny") right common carotid waveform can result from innominate stenosis.

First, a normal right common carotid waveform for comparison:

Normal right common carotid artery Doppler waveform:   Moderately broad systolic peaks and a moderate amount of flow throughout diastole. Uniphasic.

 

If there is enough stenosis in the innominate artery, then a steal phenomenon can result, with resulting biphasic waveforms, indicating back-and-forth blood flow.

If there is biphasic blood flow bilaterally, the best consideration is pulsus bisferiens (next post) from aortic insufficiency... but if it's only on the right side, it indicates a steal phenomenon in the right common carotid artery; during systole, blood flows forward into the carotid system and in diastole it flows backward into the right subclavian and arm.

In severe cases of innominate artery stenosis, there is complete flow reversal, but in less severe cases, the flow remains cephalad although an atypical biphasic waveform results... the "crouching bunny."

An example of the biphasic "crouching bunny" waveform showing midsystolic deceleration with antegrade late-systolic velocities .  Although this is is an image of the right vertebral artery, the principle and the Doppler waveform are the same in the carotid.

If the innominate artery were completely occluded, then obviously there would be complete flow reversal in the common carotid artery.

Two other points: 1) in a normal situation, carotid steal can only occur on the right side. 2) if you see abnormal right common carotid (or vertebral) waveforms, check the subclavian arteries and measure the BP in both arms.

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1. "Introduction to Vascular Ultrasonography" 5th ed.(2005) Zweibel, Pellerito, et al.
2. Tahmasebpour HR, Buckley AR, Cooperberg PL, Fix CH. "Sonographic Examination of the Carotid Arteries." November 2005 RadioGraphics, 25, 1561-1575.