Table 3.

Expected Appearances After Locoregional Therapies

Therapy	Expected Posttreatment Findings
General	A successfully treated tumor typically does not show any enhancement. Viable tumor may be present along the margins of the treated lesion as nodular or mass-like areas of APHE and/or washout. Subtraction imaging may help identify areas of viable tumor when T1 hyperintense blood products are present.
Radiofrequency Ablation (RFA) and Microwave Ablation (MWA)	After treatment, the ablation zone typically extends beyond the pretreatment tumor border, with usual margins of 5–10 mm beyond the border. For the first 3–6 months post RFA or MWA, a thin, smooth rind of enhancing peripheral liver tissue may be seen. The ablation zone shrinks around 6 months and thereafter.
	On CT, the area of ablation can be hyperdense centrally and hypodense peripherally on unenhanced images, reflecting coagulative necrosis. On MRI, post ablation blood products may be T1 hyperintense, with variable T2 signal intensity. A transient area of hyperemia in the tissue surrounding the ablated lesion, iatrogenic arterioportal shunting, and small intra-lesional air pockets are frequently seen on immediate follow-up imaging and can lead to pitfalls in interpretation [38].
Cryoablation	After treatment, the ablation zone typically extends beyond the pretreatment tumor border, with usual margins of 5–10 mm beyond the border. A thin rim of peripheral enhancement (reactive hyperemia) may be seen around the ablation zone immediately after cryoablation and can last for up to several months. Ablation zones gradually contract over time and may disappear completely or be associated with focal hepatic atrophy, including focal surface concavity or distortion of parenchymal vascular anatomy[39].
	On CT, small gas bubbles can be seen in the ablation zone immediately after treatment and can persist for up to several weeks. This should not be interpreted as infection/abscess if the patient is asymptomatic[40].
Ethanol Ablation (PEA)	The treated area may be the same size or larger than the tumor before treatment. As fibrosis and retraction within the treated area begins several months after treatment, there is a decrease in the size of the treated mass.
	On noncontrast CT, a treated mass may demonstrate air bubbles several days following treatment if the air was introduced during instillation of ethanol and for up to a month posttreatment if the air is associated with tumor necrosis (particularly if PEA was used as an adjunct to MWA or RFA) [41].
Transarterial Embolization (TAE), Transarterial Chemoembolization (TACE) and Drug eluting beads (DEB)-TACE	After treatment, a thin, smooth, linear rim of enhancement at the margin of the lesion may persist for months to years. Ill-defined regional or geographic hyperenhancement surrounding the treated tumor may be a transient post-procedural finding.
	For TAE, a noncontrast CT (NCCT) or noncontrast cone beam CT can be performed within 20 minutes of treatment completion to evaluate the postembolization tumor contrast agent retention pattern. Moderate to marked tumor contrast retention with Glisson’s sheath filling or arterial filling without defect in contrast retention is an ideal end point of embolization [42].
	With TACE, areas of oil uptake are often seen on the first follow-up at 4 weeks. Greater oil uptake by the tumor is often associated with higher tumor response rates. However, oil embolic agent (aka lipiodol or ethiodol) often make it difficult to assess enhancement on CT; both oil uptake and nonviable tumor have low signal intensity on contrast-enhanced MRI, with no enhancement on subtraction imaging [43].
	With DEB-TACE, there is transient or no retention of iodinated contrast after treatment, and drug-eluting beads are not visible on MRI [44]. Tiny foci of gas may be a normal post procedural finding for the first few days but should raise concern for infection after 1–2 weeks.
Transarterial radioembolization (TARE)	Patchy geographic enhancing regions surrounding the treated tumor can be seen for 1–5 months, most strongly in the arterial phase, mimicking infiltrative tumor. These areas may develop fibrosis and resultant atrophy at later time points.
	Compared to other intra-arterial therapies TARE is minimally embolic, and tumor enhancement can persist, even in a nodular pattern, on early follow-up imaging. Enhancement of any type (internal, nodular or rim enhancement) may not indicate residual viable tumor and should be interpreted with caution during the first 6 months after treatment [45].
External Beam Radiation Therapy (EBRT)	Typically the tumor gradually decreases in size and enhancement over several months to a year, with or without central necrosis or fibrosis [12]. The appearance of the liver parenchyma around the treated tumor evolves over time from radiation exposure at a subtherapeutic dose: congestive edema, microvascular thrombosis and sinusoidal outflow obstruction (early, < 3 months), chronic hemorrhage and hemosiderosis (~3–6 months); fibrosis, atrophy, and architectural distortion (late, > 6 months).