Hypovascular

Suh and Alexander (1939) and later Zulch (1954,1976) postulated their traditional hypothesis of a watershed zone of increased ischemic vulnerability near T4. This model was based on the relative hypovascularity of this region. 

Secondary malignant liver tumours, such as metastases of adenocarcinomas, are also hypovascular and therefore usually not identifiable by arteriography. In contrast, the metastases of malignant goitre, hypernephroid carcinoma, insulinoma and chorionepithelioma are hypervascular and therefore readily visible. 

Magnetic resonance imaging may provide additional differentiation of unclarified findings - particularly in the diagnosis of haemangioma. Hypovascular lesions are detected more easily with SPIO-enhanced MRI, whereas detection and characterization of hypervascular lesions are improved with gadolinium-enhanced MRI. (8,14) (s. tab. 36.3)... 

Yonezawa S, Asai T, Oku N (2007) Effective tumor regression by anti-neovascular therapy in hypovascular orthotopic pancreatic tumor model. J Control Release 118 303-309... 

Using three-dimensional color Doppler sonography, Fleischer et al. [36] found that hypervascular fibroids tend to decrease in size after UFE more than their isovascular or hypovascular fibroids. McLu-CAS et al. [15] showed that the initial peak systolic velocity was positively correlated with the shrinkage of fibroids and uterine volume reduction. 

An essential difference between any extracorporeal or laboratory measuring method and sensors in the body is the lack of cleaning of the measuring element. Thus, the continuous exposure of an intracorporally implanted sensor to the body tissue leads to protein build-up on its diffusion membranes and finally to a hypovascular foreign body capsule, resulting in unpredictable changes in the diffusion characteristics toward the biosensor surface. Experimental studies in animals as well as in humans have demonstrated that continuous glucose measurements over some days or weeks by means of subcutaneously implanted biosensors are at least possible. 

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... 

For the diagnosis of hepatocellular carcinoma, 3D-FISP dynamic MRI is potentially useful in the detection of HCCs, regardless of their vascularity and histological grade, because of its high contrast and spatial resolution. This indicates the usefulness of 3D-FISP in the demonstration of hypovascular as well as hypervascular lesions (Shinozaki et al. 2002). 

Indications Loco-regional therapies are indicated in the treatment of hepatic malignancy in those patients with disease limited to the liver who are not candidates for resection. Both primary and secondary hepatic neoplasms that are hypervascular in nature respond more favorably to chemoemboUzation than those lesions that are hypovascular. Patient selection is crucial to reduce treatment-related complications such as hepatic infarction, abscess or biloma formation, liver failure, and cholecystitis (Chung et al. 1996 Sakamoto et al. 1998 Song et al. 2001). 

For example, in a patient with a hypervascular carcinoma of the uterine cervix as defined by angiography through catheters placed in the main trunk of the internal iliac arteries, the radionuclide flow study can be utilized to demonstrate the flow distribution almost exclusively to the true pelvis. Therefore, the position of the catheters would be adequate and more selective catheterization would not be necessary. On the other hand, in a patient with a hypovascular tumor (most squamous cell carcinomas of the cervix are relatively hypovascular), catheter placement into the internal iliac artery may not only infuse the true pelvis, but may also infuse the buttocks. Embolization of the superior and inferior gluteal arteries with coils or segments of Gelfoam or both can be used to prevent the infusion of the buttocks and redistribute the chemotherapy to the true pelvis. This may result in increased pudendal flow and potentially increase local toxicity. 

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. 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-...

MDCT of the pancreas is performed using triphasic acquisition obtained prior to, and biphasic acquisition after, intravenous contrast material injection (Freeny 2005). It has been shown that an arterial-phase scan (similar in timing to the typical arterial-phase scan of the hver) is not of value for detection of pancreatic adenocarcinoma (Fletcher et al. 2003 Graf et al. 1997). Pancreatic adenocarcinoma, which is by far the most common pancreatic tumor, is hypovascular and shows only little to no contrast to the minimally enhancing pancreatic parenchyma in the early arterial phase. Lu et al. (1996) implemented a two-phase CT protocol evalu-... 

Higher contrast material flow rates have been shown to be advantageous. Tublin et al. (1999) showed that a flow rate of 5 ml s is superior to 2.5 ml s regarding enhancement of the pancreas and the fiver parenchyma. Many authors recommend using a flow rate of 4-5 ml s to optimize pancreatic enhancement and tumor-to-pancreas contrast Schueller at eh (2006) demonstrated that an even higher flow rate of 8 ml s (compared with the standard flow rate of 4 ml s ) has its merits. They demonstrated that a flow rate of 8 ml s results in better enhancement of the pancreas, but not of the typically hypovascular adenocarcinomas, which resulted in a higher tumor-to-pancreas contrast. 

As regards the location of the degenerative areas, the increased risk of certain anatomic sites for development of tendinosis has led to the concept of critical zones, in which several factors, such as aging, hypovascularization, and biomechanical effects in combination with repetitive trauma, play a specific causative role (Kainberger et al. 1997 Schepsis et al. 2002). In the Achilles tendon, for example, the predominant involvement of its middle third has been attributed to the fact that this is an area of low vas-... 

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