Hypovascular metastases

Fig. 7.38a,b. Distant metastases. a, b Contrast-enhanced CT images. Numerous hypovascularized metastases are seen in the liver. In addition, metastatic spread to the peritoneum (asterisk) and extensive para-aortic lymph node metastases. FIGO stage IVB... 

Fig. 29.6. CT images in the portovenous phase of two different patients suffering from extrahepatic malignancies with liver metastases. On the kft side, typical hypovascular metastases from a breast cancer are depicted (arrows) the larger lesions show central regressive changes with the corresponding bull s-eye appearance. On the right side, a metastasis from a colorectal carcinoma is shown (arrow). This lesion is also a typical hy-...

Non-hepatopathic patient History of neoplasia (suspected hypovascular metastases) + + -... 

Doppler typically shows no or some peripheral vascularity in hypovascular metastases, while hy-pervascular deposits may show vessels throughout the lesion (Fig. 18.1). Use of Doppler can be useful to differentiate metastases from FNH and focal fatty change/infiltration large FNH (>approx. 4 cm) often shows a typical spoke-wheel arterial pattern, often within a central scar (Fig. 18.1) focal fatty change/sparing shows no abnormal vascularity and normal hepatic vessels crossing the lesion with no deviation. 

Metastases show characteristic dynamic features in all three phases after contrast injection (Figs. 18.4-18.6). In the arterial phase the appearances are twofold hypovascular metastases show... 

Liver abscesses are rare they may, however, be confused with metastases since they also show a rim enhancement in the arterial phase and produce enhancement defects in the later phases. An important differential diagnostic clue is the complete absence of vessels and enhancement in the central liquid portion of an abscess, while even hypovascular metastases will display some weak but visible central enhancement due to small vessels, provided they are not necrotic. 

Although quadruple-phasic contrast-enhanced MDCT protocols have been advocated, most authors prefer two or maximum three different contrast-enhanced phases, depending on the indication, i.e. three-phasic protocols evaluation of suspected of HCC (Loyer et al. 1999). Whether an unenhanced scan is still of value, is under discussion (Kopka et al. 2000 Oliver et al. 1997). No or only limited role of unenhanced scan were found for the evaluation of hypervascular or hypovascular hepatic metastases (Patten et al. 1993 Paulson et al. 1998 Sheafor et al. 1999 Sica et al. 2000). However, Oliver et al. (1998) found that 28% of all hepatic metastases were seen only on the unenhanced scan. At our institution, unenhanced scan is performed in baseline studies, because the differentiation between cysts and small hypovascular metastases and a delineation of calcifications and hemorrhage is improved (Fig. 19.1). 

Hypervascular metastases exhibit an early, brief and pronounced signal enhancement in the arterial phase, which fades rapidly in the later phases. These lesions appear hyperintense in the arterial phase, but other hypervascular lesions like HCC, adenoma and FNH may show similar pattern. Hypovascular metastases exhibit a delayed contrast enhancement, which means they appear hypointense in the arterial phase. A maximal lesion-to-liver contrast is reached in the PVR The equilibrium phase is still important, because it can be used for lesion differentiation (i.e. hemangioma versus metastasis). Hemangiomas show persistent enhancement during the equilibrium phase, whereas most metastases appear iso- or hypointense compared to liver parenchyma (Fig. 19.3). 

In general, the vascularity of metastases is classified according to their contrast behavior in the arterial-dominant phase scan. Metastases which are hyperdense to normal liver parenchyma in this phase are called hypervascular . Hypervascular metastases are less frequently than hypovascular metastases in the liver and typically originate from renal cell carcinomas, carcinoids, pancreatic islet cell carcinomas, sarcomas, pheochromocytomas, melanomas, thyroid carcinomas, chorion carcino-... 

Fig. 19.8a,b. Hypovascular metastases of metastatic adenocarcinoma, a In the arterial phase the small lesions throughout the liver are only faintly visible, b In the portal-venous phase scan, diffuse metastatic spreading in the liver is well demonstrated... 

According to the literature, fiver metastases can be detected with spiral CT with a sensitivity ranging from 58 to 85% (Lencioni et al. 1998 Ward et al. 1999 Vales et al. 2001 Bartolozzi et al. 2004). In case of hepatic steatosis, lower detection rates are described due to the missing contrast between typical hypovascular metastasis and the hypodense fiver parenchyma in steatosis (Kato et al. 1997 Llauger et al. 1991). 

Fig. 2.10a,b. Typical pattern of hypovascular colorectal cancer metastasis, a Lesion is hypodense on unenhanced image, b Lesion remains hypodense 60 s after i.v. administration of contrast medium... 

Fig. 18.5a-d. Dynamic features of a hypovascular hepatic metastasis from a breast primary after contrast injection (SonoVue). a Slightly hyperechoic lesion with hypoechoic halo and small central necrosis on unenhanced US. b In the arterial phase the lesion displays strong peripheral rim enhancement (arrow), c Portal venous phase imaging shows fading of the rim. d In the delayed phase, the lesion shows as a hypoechoic enhancement defect... 

---