From the SIR Residents and Fellows Section (RFS)

Teaching Topic: The Use of Denver Shunts to Manage Chylous Ascites.

Yarmohammadi H, Brody LA, Erinjeri JP, et al. Therapeutic Application of Percutaneous Peritoneovenous (Denver) Shunt in Treating Chylous Ascites in Cancer Patients. J Vasc Interv Radiol 2016; 27: 665-673.

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This manuscript revaluates the safety and efficacy of percuntaneous and peritoneovenous shunt (PPVS) placement in treating intractable chylous ascite (CA) in patients with cancer. The study from Memorial Sloan-Kettering Cancer Center involved 28 patients with refractory CA. The authors report resolution of ascites or symptom relief in 92% of patients with statistically increased levels of serum albumin in the PPVS placement group. The reported complication rate was 37% with shunt malfunction/occlusion being the most common at 22%. Both smaller venous limb size and presence of peritoneal tumor were associated with higher rates of shunt malfunction.

Clinical Pearls

How does chylous ascites (CA) form?

This study focused on CA (milky appearance of the ascites with an ascitic fluid triglyceride concentration > 110 mg/dL) as a complication of surgical therapy for urologic malignancy, which requires retroperitoneal lymph node dissection (LND). Post-surgical CA can form early, due to damage to the lymphatics themselves, or late, due to adhesions and extrinsic compression on the lymphatic system. Other causes include: malignant compression on lymphatic vessels, cardiovascular disease, such as right heart failure, causing increased lymphatic pressure, hepatic cirrhosis causing disruption of serosal lymphatic channels, infections, such as peritoneal tuberculosis and filariasis, congenital conditions, such as primary lymphatic hypoplasia and Klippel-Trenaunay (lymphatic hypoplastic malformations), or inflammatory conditions such as radiation injury and acute or chronic pancreatitis.

What treatment options are available and how does the Denver shunt work?

Traditionally, CA is managed by conservative diet modification, involving a high-protein, low-fat, medium-chain triglyceride (MCT) oral diet or total parenteral nutrition. Dietary restriction of long-chain triglycerides (LCT) avoids their conversion into monoglycerides and free fatty acids (FFA), which require transport as chylomicrons via intestinal lymph ducts. By contrast, MCTs are absorbed directly into intestinal cells and transported as FFA and glycerol directly to the liver via the portal vein. One of the main problems with conservative management and paracentesis is loss of nutrients and the risk of developing malnutrition. Pharmacological agents, such as somatostatin and octreotide, have been shown to be successful in treating chylous ascites. Paracentesis is performed as needed to palliate symptoms. Peritoneovenous shunt (PVS) placement for treatment of refractory ascites was first described by Smith in 1962. The Denver shunt (CareFusion Corporation, San Diego, California) pump is percutaneous PVS (PPVS) that is either single-valved or double-valved. These shunts redistribute ascitic fluid from the abdomen into the central circulation based on a pressure gradient between the abdomen and central venous system and incorporate a compressible valve chamber between the peritoneal limb and the venous limb to prevent reflux of fluid back into the peritoneal cavity, providing unidirectional flow.

Questions to consider

When should PPVS placement and removal be considered?

Persistent or refractory CA not responding to 2 weeks of conservative treatment and repeated paracentesis was the threshold for PPVS placement in this study. Patients’ high-protein, low-fat diet was switched to a regular diet after the procedure. Patients were instructed to pump the shunt 20 times, twice a day, once in the morning and once before bedtime while in the supine position. Initial symptomatic relief (abdominal distention) was evaluated at the 1-week visit and was achieved in 100% of patients. CA permanently resolved in patients with urologic malignancies, whose ascites had resulted from retroperitoneal LND. In the remaining 15 patients, palliation of symptoms until shunt removal or death was achieved in 13 (87%). Based on the results of the present study, the recommendation is that when a patient experiences changes in pump consistency and there is no clinical or radiographic evidence of ascites, the shunt can be removed.

What complications should be considered for PPVS?

Reported complications of PPVS placement include shunt occlusion, gastrointestinal tract (variceal) bleeding, infection, and DIC. The most common complication in this study was PPVS malfunction/occlusion (21%). Using a large venous limb (15.5F) was noted to occlude less than systems using a 11.5F venous limb. Patients with peritoneal tumors (lymphangioleiomyomatosis [LAM] and peritoneal mesothelioma) should be expected to have repeated occlusions. Two patients (7%) developed asymptomatic or subclinical DIC. One proposed reason for development of DIC is rapid introduction of the ascitic fluid containing high levels of fibrin-rich procoagulants, including endotoxin, thromboplastin activated clotting factors, and plasminogen activator, into the central venous system. In CA, the main reason for ascites formation is leakage of chyle secondary to the obstruction or disruption of the lymphatic system and returning the chylous fluid back into the circulation is actually physiologic. The authors have suggested limiting the risk of DIC by draining the ascites to completion at the time of shunt placement and replacing the ascitic fluid with 4L of normal saline to avoid putting into circulation a large amount of potentially DIC-inducing substances.

Post Author:
Rajat Chand, MD
Diagnostic Radiology Resident, R-1
John H. Stroger Jr. Hospital of Cook County

From the SIR Residents and Fellows Section (RFS)

Teaching Topic: Position Statement on Noninvasive Imaging of Peripheral Arterial Disease by the Society of Interventional Radiology and the Canadian Interventional Radiology Association

Dhanoa D, Baerlocher MO, Benko AJ, Benenati JF, Kuo MD, Dariushnia SR, Faintuch S, Midia M, Nikolic B. Position statement on noninvasive imaging of peripheral arterial disease by the Society of Interventional Radiology and Canadian Interventional Radiology Association. J Vasc Interv Radiol. 27: 947-51.

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This manuscript reviews and provides recommendations for noninvasive lower-extremity imaging of PAD. This includes both functional and anatomic tests. The functional or physiologic tests include the ankle-brachial index (ABI), segmental limb pressures, pulse volume recordings (PVRs), segmental Doppler waveforms, and oxygen testing. The anatomic tests include duplex ultrasound (US), computed tomography (CT), and magnetic resonance (MR) imaging. Because of the complexities and degree of discussion needed for each study, CT and MR imaging will be discussed in a future manuscript. Given changes to our delivery of healthcare in the United States, the manuscript serves an important role in defining the appropriate use of noninvasive imaging to improve patient selection and documenting post-procedure outcomes.

Clinical Pearls

What imaging modalities constitute a complete noninvasive examination of peripheral arterial disease?

A typical noninvasive examination should always include an ABI with concomitant pulse volume recordings (PVRs), continuous-wave Doppler analysis, segmental pressures, and exercise testing.

Why is a position statement on noninvasive imaging of PAD needed?

The implementation of the Affordable Care Act has brought about drastic changes to the reimbursement models for medicine. Alternative methods have emerged to enact the intended paradigm shift towards value-based and outcome-oriented delivery of healthcare instead of the standard, traditional merit-based fee-for-service model. Thus, the appropriate use of noninvasive imaging to improve pre-procedural patient selection, as well as to objectively document post-procedure outcomes, is of critical significance.

Questions to Consider

How are ABIs calculated and how are results utilized to grade PAD?

ABIs are calculated by dividing the ankle systolic blood pressure by the brachial artery systolic blood pressure. Both upper extremity BP are obtained and the higher of the two are utilized. For the ankle systolic BP, the greater of the dorsalis pedis or posterior tibial artery should be used.

If there is a >15mmHg discrepancy between the upper extremity systolic blood pressures, hemodynamically significant disease should be considered to be present proximal to the brachial artery with the lower systolic blood pressure.

Stielger et al. proposed an ABI-Based Grading Scale as follows:

• >1.3 : Falsely high value (suspicious for medial sclerosis) 
• 0.9-1.3 : Normal 
• 0.75-0.9 : Mild PAD 
• 0.4-0.75 : Moderate PAD 
• <0.4 : Severe PAD 

What are the important limitations to ABIs?

ABIs can be falsely elevated in patients with heavily calcified arteries. In these circumstances, it is recommended that toe brachial index be utilized as calcifications are rarely found at the great toe. A TBI of >0.65 is considered normal and TBI < 0.4 is considered severe PAD.

What are the four phases of a normal typical waveform in segmental PVR?

The four phases are:

1. A rapid systolic upstroke
2. Rapid diastolic downstroke
3. Prominent dicrotic notch (*The dicrotic notch denotes the closing of the Aortic Valve)
4. Normalization to baseline before the next cycle

How do you interpret arterial Doppler waveforms?

Normal arterial Doppler waveforms are triphasic consisting of a sharp systolic upstroke, reversal of flow below baseline and then a short forward component in late diastole. Mild PAD leads to a bisaphic waveform in which the short forward component in late diastole is lost. As PAD progresses to severe disease, the waveform continues to flatten and becomes monophasic with loss of the flow reversal. The waveform becomes rounded with a slow upstroke and slow downstroke creating the classic postobstructive tardus parvus signal.

Post Author:
Andrew Niekamp, MD
Diagnostic Radiology Resident, PGY-3
UT Houston

From the SIR Residents and Fellows Section (RFS)

Teaching Topic: Endovascular Repair of Celiac Artery Aneurysm with the use of Stent Grafts

Zhang W, Fu YF, Wei PL, E B, Li DC, Xu J. Endovascular repair of celiac artery aneurysm with the use of stent grafts. J Vasc Interv Radiol. 2016. 27 (4): 514-8.

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A recent article in JVIR evaluated the feasibility, safety, and long-term outcome of stent-graft insertion for endovascular repair of celiac artery aneurysms (CAAs). 10 patients with CAAs underwent endovascular repair via stent-graft insertion in a single center. Follow-up CTAs were performed at 1, 3, 6, and 12 months. There was no evidence of endoleak, stent obstruction, or splenic infarction during the follow-up period and all 10 patients had CAA sac shrinkage or increased CAA sac thrombus on follow-up imaging.

Clinical Pearls

What do we know about aneurysms involving visceral arteries?

Visceral arterial aneurysm (VAA) are rare, with an incidence of 0.1%–2%. Celiac artery aneurysms (CAA) constitute 4.8%–6.3% of all VAA cases. In this study, the treated aneurysms varied from 2.1 x 1.6 cm to 8.8 x 7.1 cm. They frequently present as a life-threatening emergency and are often fatal if associated with rupture. An aneurysm ≥ 20 mm in size is considered sufficient to warrant treatment if the patient’s overall condition permits it. Recent studies have reported treatment options for CAAs consisting of open surgery or embolization. Few publications have reported stent-graft insertion for endovascular repair in patients with CAAs.

What does the data show on endovascular treatment vs. open surgery?

In a recent article by Shukla et al. comparing outcomes between endovascular treatment (n = 122) and open surgery (n = 59) for VAAs, results show that endovascular treatment and open surgery are equally durable for patients with intact VAA, but endovascular treatment for ruptured VAAs was associated with a lower 30- day mortality rate (7.4% vs 28.6%; p<0.05) and better 2-year overall survival (69.4% vs 46.4%; p<0.05).

Questions to Consider

What are possible complications of CAA aneurysms and Stent Grafts for the CAA?

As mentioned above, the most dangerous complication of untreated CAAs is life-threatening hemorrhage. However, endovascular treatment of CAAs with stent grafts carries its own set of risks including dissection, stent thrombosis with end-organ ischemia, splenic infarction, and endoleaks.

While performing an endovascular Stent Grafting of a CAA, what do you have to watch for?

The anatomy of celiac artery aneurysms is complex, given that multiple branches can exit the aneuryms. Without identifying and potentially embolizing relevant branches, endoleaks may develop after stent graft placement. Equally, the interventionalist must define the distal landing zone for the endograft to assure a good seal and likelihood of long term patency. Pre-procedure planning with CTA and detailed catheter angiography are of utmost importance. As mentioned previously, endoleaks are of a concern as well, however, none resulted in the cases presented in the manuscript above. Many CAAs are associated with median arcuate ligament compression and post-stenotic dilation. Ligamentous compression may permanently deform balloon expandable stent grafts,

What are the limitations of the above study and why?

While the study sample was small (n=10), given low prevalence of the disease, this is nevertheless a meaningful number to show safety and efficacy. In addition, the retrospective nature introduces the possibility of selection bias. Can all CAAs be treated with stent graft? What can preclude a CAA from stent graft repair? If a CAA may be treated by embolization or stent graft, how should we decide the optimal treatment approach? 

What are the different types of Endoleaks?

While the classification system for endoleaks was originally intended for and applied to abdominal aortic aneurysms (AAAs), it can be used for discussion regarding stent graft treatment for aneurysm exclusion in other vascular territories.

Type I: Persistent filling of the aneurysm sac due to incomplete seal at the proximal or distal end of the stent graft.
Type II: Persistent filling of the aneurysm sack due to retrograde branch flow from collateral vessels.
Type III: Blood flow into the aneurysm sac due to ineffective sealing of overlapping graft joints.
Type IV: Blood flow into the aneurysm sac due to the porosity of the graft fabric, causing blood to pass through the graft joints or rupture of graft fabric.
Type V: Aneurysm sac expansion without clear evidence of endoleak origin.

Additional citations:
Shukla AJ, Eid R, Fish L, et al. Contemporary outcomes of intact and ruptured visceral artery aneurysms. J Vasc Surg 2015; 61:1442–1448.

Post author:
Ali Alikhani, MD
Diagnostic Radiology Resident, PGY-4
University of Tennessee Methodist Healthcare