Interventional Radiology I: Cross-Sectional Imaging Procedures

What are the indications for image-guided percutaneous needle biopsy (PNB)?

• Establish a benign or malignant diagnosis of a lesion.

• Stage patients with known or suspected malignancy when metastasis is suspected.

• Obtain material for microbiological analysis in patients with known or suspected infection.

• Determine the nature and extent of diffuse parenchymal diseases (e.g., cirrhosis, organ transplant rejection, glomerulonephritis).

What are the indications for image-guided percutaneous fluid aspiration (PFA) and percutaneous catheter drainage (PCD)?

• Obtain a sample for fluid characterization.

• Remove fluid suspected to be infected or the result of an abnormal fistulous connection.

• Remove a fluid collection suspected to be the cause of symptoms sufficient to warrant drainage.

• Perform an adjunctive procedure necessary to facilitate the improved outcome of a subsequent intervention (e.g., drainage prior to sclerotherapy).

• Perform a temporizing maneuver to stabilize the patient’s condition before definitive surgery (e.g., drainage of diverticular abscess to allow primary reanastomosis).

Name contraindications (absolute or relative) for image-guided PNB and PFA/PCD.

• A competent patient who does not give consent

• A patient who is unwilling or unable to cooperate with or to be positioned for the procedure (e.g., a retroperitoneal abscess is only accessible percutaneously via the back but the patient is unable to lie prone because of pain from an anterior abdominal wound or recent surgical incision)

• Uncorrectable coagulopathy

• Severely compromised cardiopulmonary function or hemodynamic instability

• Lack of a safe percutaneous “window” or pathway to the target

• Inability to visualize the target with available imaging modalities

• Pregnancy in cases in which imaging guidance uses ionizing radiation (the potential risks to the fetus and the clinical benefits of the procedure should be considered before proceeding)

When is an image-guided percutaneous core biopsy required as opposed to a percutaneous fine-needle aspiration (FNA)?

When architectural detail is needed for histopathologic diagnosis (e.g., well-differentiated neoplasms) and staging (e.g., staging fibrosis of diffuse liver diseases), a core biopsy is required. FNA specimens are usually obtained using 22- to 25-gauge needles and yield clusters of cells and occasionally small tissue fragments for cytopathologic examination. Core biopsies are performed using disposable, spring-loaded, automated devices (20 gauge or larger) and yield cylinders of tissue 1 to 2 cm long.

Which imaging modalities are used to guide interventional procedures?

Fluoroscopy, ultrasound (US) ( Figure 67-1 ), computed tomography (CT), and magnetic resonance imaging (MRI) can be used to guide interventions. US and CT are used most often.

What five conditions must be satisfied before a percutaneous procedure can be performed?

• The patient or patient representative must provide written, informed consent for the procedure, intravenous conscious sedation (if applicable), and potential administration of blood or blood products.

• Code status during the procedure and postprocedural recovery period must be determined if the patient has do not attempt resuscitation orders.

• The patient’s coagulation profile must be determined and any coagulopathies corrected.

• The patient must be fasting if conscious sedation will be used during the procedure. Exact times vary depending on institutional protocols and guidelines. Typical guidelines are fasting for at least 2 hours for “clear” liquids and at least 6 hours for “solids” or food.

• Appropriate antibiotic coverage must be administered if there is any possibility that the lesion or fluid collection is infected.

What coagulation parameters are assessed before a percutaneous procedure?

The patient history should be reviewed for bleeding risks, such as anticoagulant (warfarin [Coumadin], low-molecular-weight heparin) or platelet-inhibitor (aspirin, clopidogrel [Plavix]) agents, uremia, or hepatocellular disease. Routinely assessed parameters include hematocrit, prothrombin time, international normalized ratio (INR), partial thromboplastin time (PTT), and platelet count.

How and when should coagulopathies be corrected?

Coagulopathies should be corrected with appropriate transfusions of packed red blood cells or hemostatic agents such as platelets, fresh-frozen plasma, vitamin K, cryoprecipitate, protamine, and recombinant factor VIIa. Institutional guidelines vary, but an INR greater than 2, a PTT greater than 1.5 times normal, or a platelet count less than 50,000/μL are each a relative contraindication for most procedures. Recent Society of Interventional Radiology guidelines offer useful coagulation and transfusion parameters for percutaneous procedures based on low, moderate, and significant risk of bleeding and ease of bleeding detection and controllability. If the patient has a coronary stent, a cardiology consult may be necessary prior to discontinuing antiplatelet agents to avoid stent complications.

What pharmacologic agents can be injected into septated or viscous abdominal fluid collections to improve drainage?

Intracavitary fibrinolysis therapy with tissue plasminogen activator (tPA) can be performed through the drainage catheters to shorten treatment time and improve the clinical course of patients treated with percutaneous drainage catheters. Optimal dosing regimens have not been determined. Typical doses of tPA range from 2 to 6 mg of tPA diluted in 10 to 50 mL saline. The total volume of fluid depends on the size of the cavity. The dose is injected into the catheter, which is clamped for 1 to 2 hours after the dose is administered. After unclamping, the dose is allowed to drain spontaneously. The dose can be administered 1 to 3 times daily. Total number of doses varies depending on output response. Caution should be used with hepatic abscesses or in patients who are coagulopathic because of the potential increased risk of bleeding.

What should you suspect if the drainage catheter has persistently elevated outputs?

If a catheter has persistently elevated outputs, a sudden increase in drainage, or a change in the composition of the effluent, a fistula should be suspected. Injection of contrast into the catheter under fluoroscopy often demonstrates the fistula, which can be to the gastrointestinal tract, pancreatic duct, biliary system, or to the genitourinary tract. Occasionally, an alternative study is necessary such as a small bowel follow-through if the fistula acts as a one-way valve and is not demonstrated by injection of the drainage catheter. Often the fistula will heal but prolonged drainage is required and can last as long as 2 to 4 weeks or more. The catheter should not be removed until the fistula has healed or has been repaired.

When should you remove the drainage catheter?

If the catheter output is less than 10 to 20 mL per 24 hours, there are no other reasons for the decreased outputs (e.g., catheter clogged, kinked, or malpositioned), and the patient has clinically improved, the catheter can be removed. Repeat imaging with US, CT, or contrast injection under fluoroscopy is not necessary unless the patient has a known fistula or is still clinically symptomatic, or unless the overall output is less than expected. An exception to these criteria for catheter removal is percutaneous cholecystostomy catheters. Percutaneous cholecystostomy catheters require an epithelialized tract to form before removal to prevent bile leakage and bile peritonitis. This usually requires a minimum of 3 weeks’ time, but if the patient is immunocompromised or in the intensive care unit, the process can take even longer.

What are the major complications of image-guided PNB?

Major complications are defined as those that result in an unplanned increase in the level of care, prolonged hospitalization (in-patients), admission to the hospital for therapy (out-patients), permanent adverse sequelae, and death. The complications of PNB can be stratified as general or organ-specific. Major general complications include hemorrhage, infection, solid organ injury, bowel perforation, and pneumothorax. Reported rates of major complications range from 0.1% to 10% with infection as a result of a biopsy being uncommon. Clinically significant bleeding requiring blood transfusion or intervention is infrequent, but the reported rates increase with larger needles sizes, use of cutting needles, and the vascularity of the organ or lesion biopsied.

Does seeding of the needle tract occur during routine tumor biopsy?

Case reports of tumor spread along the needle tract as a result of percutaneous biopsy are described in the medical literature. Overall, seeding the needle tract is uncommon and the reported rates vary according to organ biopsied. For masses suspected to be hepatocellular carcinoma (HCC), needle track seeding can be a potentially devastating complication in transplant candidates in whom immunosuppression may predispose to seeded tumor growth; however, the American Association for the Study of Liver Diseases believes the risk has been overstated in earlier literature. Needle gauge sizes, number of needle passes, and coaxial versus single-needle systems are believed to influence the risk of tumor seeding, but robust evidence is still lacking. Although this potential complication should be discussed with the patient prior to the procedure, it should not be considered a contraindication to FNA or core biopsy in patients in whom the diagnosis is in question and when knowledge of a specific diagnosis is likely to alter clinical management.

Cystic lesions like suspected cystadenomas or cystadenocarcinomas of the ovary or pancreas should not be sampled percutaneously, even with small, skinny needles. This is associated with a significant risk of postprocedure needle-tract seeding and subsequent pseudomyxoma peritonei or peritoneal carcinomatosis.

Is FNA or core biopsy safe or necessary for all hepatic masses?

Benign masses such as hemangiomas ( Figure 67-2 ), focal nodular hyperplasia, and adenomas often have distinguishing characteristics on high-quality cross-sectional imaging modalities. When these masses are present in patients with classic corresponding clinical features, obtaining specimens for cytologic or histologic examination is usually not necessary. If any imaging or clinical features are not characteristic, biopsy can be performed safely.

Carcinoid crisis characterized by profound hypotension can be precipitated by FNA of hepatic carcinoid metastases. Patients with carcinoid tumors typically present with characteristic clinical symptoms and can be confirmed biochemically. If biopsy of a suspected hepatic carcinoid metastasis must be performed for diagnosis, appropriate preparatory measures should be taken and resuscitative equipment needs to be readily available.

How are pyogenic hepatic abscesses treated?

At least 90% of pyogenic hepatic abscesses can be successfully drained percutaneously. Most pyogenic abscesses smaller than 3 cm in diameter are treated with antibiotics either alone or in combination with needle aspiration, with excellent success rates. For pyogenic abscesses larger than 4 cm in diameter, image-guided PCD is required. The size of the self-retaining, pigtail catheter inserted often depends on the viscosity of the fluid encountered.

The possibility of an abscess complicating an underlying hepatic neoplasm should always be considered. Follow-up imaging should be obtained to document eventual complete resolution of the lesion. FNA or core biopsy of any persistent abnormality may be necessary to exclude occult hepatic tumor.

When is image-guided PFA/PCD indicated for treatment of amebic abscesses ( Figure 67-3 )?

Amebic abscesses respond well to appropriate antibiotic treatment regardless of size, and PCD is usually not required unless response to medical treatment is inadequate. PCD should be considered for large amebic abscesses in a peripheral location or in the left hepatic lobe as these sites are prone to rupture into the peritoneum, pericardium, or pleural space.

Is image-guided PFA/PCD indicated for treatment of hydatid cyst disease?

Cystic echinococcosis is caused by Echinococcus granulosus. Previously PFA/PCD of a suspected echinococcal cyst or hydatid cyst disease was an absolute contraindication because of fatal anaphylaxis from spillage of the scolices. However, published series describe favorable results with oral albendazole treatment combined with PCD or with the puncture, aspiration, injection, reaspiration (PAIR) technique. The cyst contents are aspirated via the percutaneous puncture. Contrast is injected under fluoroscopic guidance to ensure there is no communication with the bile ducts and then a protoscolicide such as hypertonic saline or ethanol is injected, allowed to sit, and then reaspirated. Modified PAIR uses placement of a catheter, which allows more complete evacuation of the endocyst and repeat injections of protosolicide, and is especially useful for treating large cysts. Oral albendazole treatment must be started at least 4 hours prior to percutaneous intervention. Caution: The risk of fatal anaphylaxis is not entirely eliminated and thus appropriate emergency medical treatment and resources must be readily available ( Figure 67-4 ).

Describe the treatment of simple, benign, epithelialized hepatic cysts.

Epithelialized hepatic cysts can be drained successfully and obliterated with sclerotherapy. A self-retaining, pigtail catheter can be used. After catheter placement with US or CT guidance, and complete cyst aspiration, samples are sent for culture and cytologic examination. Contrast is injected through the catheter under fluoroscopic guidance to ensure that there is no communication with the biliary tree. If no connection to the bile ducts is demonstrated, then 33% to 50% of the original cyst volume is replaced with a sclerosant. Sclerosants used to treat hepatic cysts include ethanol (not to exceed 100 mL), tetracycline, doxycycline, and povidone-iodine. The patient is rotated into multiple positions until the entirety of the cyst wall has been in contact with the sclerosing agent for 60 minutes. The entire volume of sclerosant and residual cyst contents are then completely aspirated through the catheter. Large cysts may require repeat treatments. After the final treatment and aspiration, the catheter is removed.

Can cysts in patients with polycystic liver disease be treated with sclerotherapy?

Yes, although solitary hepatic cysts are more often successfully sclerosed than cysts in patients with polycystic liver disease. In polycystic liver disease, cysts tend not to collapse, presumably because the surrounding liver is less pliable, making cyst wall apposition and subsequent scarring of the cavity less likely. Surgical or laparoscopic unroofing, fenestration, or removal of cysts may be needed when percutaneous treatment fails.

Name the minimally invasive percutaneous ablative therapies for HCC.

Percutaneous ablative techniques for local control of HCC can be divided into two categories: thermal ablation and chemical ablation. Thermal ablation techniques alter the temperature of the tumor to cause cell death and include heat-based methods (radiofrequency ablation [RFA], microwave ablation ( Figure 67-5 A-D ), laser ablation, high-intensity focused US) and cold-based methods (cryoablation). Chemical ablation involves injecting substances such as ethanol or acetic acid directly into the tumor to produce tissue necrosis.

What temperatures must be achieved to be cytotoxic for tumor destruction?

Irreversible damage with cellular protein denaturation, cell membrane dysfunction, and coagulation necrosis occurs at temperatures between 60 ° C and 100 ° C. Above 100 ° C to 110 ° C, tissue carbonization and charring occurs which results in diminished volume of the ablation zone from less effective energy transmission. In cryotherapy, irreversible damage from cellular dehydration, membrane rupture, and ischemic microvascular thrombosis occurs at temperatures between −20 ° C and −40 ° C. For adequate tumor destruction, the entire target volume must be subject to cytotoxic temperatures and thus the zone of ablation must be larger than the size of the tumor itself to achieve tumor-free margins.

What are the advantages of RFA and other methods of percutaneous thermal ablation?

• Low mortality and complication rates (Multicenter surveys report mortality rates ranging from 0.1% to 0.5%, major complication rates ranging from 2.2% to 3.1%, and minor complication rates ranging from 5% to 8.9%.)

• Repeatability

• Minimally invasive and shorter recovery times compared with surgery

• Can be used in combination with other treatment therapies

• Less destruction of nonneoplastic tissue than surgery

What are the contraindications of RFA or percutaneous thermal ablative techniques?

The only absolute contraindications are uncorrectable coagulopathy or a noncompliant patient. RFA and other percutaneous ablative techniques are local treatments and are usually not performed in patients with vascular invasion or extrahepatic metastases. Patients with colonization of the biliary tract from bilioenteric anastomoses, endoscopic sphincterotomy, or bilioenteric fistula are at increased risk of postablation liver abscess. Some liver transplant centers may exclude patients from transplant consideration who have had percutaneous tumor ablation because of concerns of tumor recurrence from tract seeding, so it is important to discuss treatment options with referral hepatologists and surgeons who are experts in liver transplantation.

Describe the risks of thermal ablation related to the anatomic location of the tumor.

Superficial tumors adjacent to the gastrointestinal tract are at risk for thermal injury to the bowel wall. The colon appears to be at greater risk for perforation than the stomach and small bowel because of the thinner wall thickness and its lesser mobility. The gallbladder and biliary tract are also at risk for thermal injury. Perforation of the gallbladder is rare, but ablation of tumors adjacent to the gallbladder can be associated with iatrogenic cholecystitis, which is usually self-limited. Bilomas and biliary stenoses can also occur. Lesions in the dome of the liver can result in thermal injury to the diaphragm, pneumothorax, or hemothorax. Vessels in the vicinity or adjacent to lesions are usually protected because of the “heat or cold sink” effect of flowing blood. However, if the vessel is very small or the flow is decreased for any reason, thrombosis can occur. The heat or cold sink effect may also result in incomplete ablation of the neoplastic tissues adjacent to the vessel from temperature loss.

In the treatment of HCC, how do survival outcomes of RFA compare with surgical resection?

Most studies evaluating surgical resection and RFA show similar long-term outcomes for HCC smaller than 3 cm. In a randomized control trial of 112 patients with a solitary HCC less than 5 cm by Chen et al., there were no significant differences in local recurrence, overall survival, or disease-free survival between the two groups.

What other liver tumors have been treated with percutaneous thermal ablative techniques?

Liver metastases from neuroendocrine, gastric, pancreatic, pulmonary, renal, uterine, or ovarian cancer and melanoma have all been successfully treated with RFA. Besides HCC, the majority of percutaneous thermal ablative procedures are performed for the treatment of colorectal liver metastases. Percutaneous RFA has also been used to successfully treat symptomatic giant cavernous hemangiomas in patients choosing not to undergo surgical resection.