Parenchymal enhancement

Several investigators have described the time course of contrast enhancement with gadolinium chelate in patients with ischemic stroke (Crain et al. 1991 Elster 1991 Essig et al. 1996 Karonen et al. 2001 Vo et al. 2003). Contrast-enhanced MRI on days 1, 2 and 7 post-stroke revealed two different patterns, namely intravascular and parenchymal enhancement of the contrast agent. Whereas intravascular enhancement in the infarcted area was detected in 78% of the cases on day 1 and in 30% of cases at 1 week, parenchymal enhancement was observed with increasing frequency over 7 days (Karonen et al. 2001). 

Also technical aspects may contribute to the variable incidence of parenchymal enhancement in acute human stroke. With double dose contrast medium and a time lag between injection and imaging, every fourth stroke patient showed tissue enhancement within 24 h of stroke onset (Karonen et al. 2001). Widespread parenchymal enhancement in Tl-w images seems to gradually develop over the first week when simultaneously the diffusion changes tend to pseudonormalize. Without precise clinical history confounding with tumor enhancement may occur and should be ruled out by observation of the time profile of MR contrast enhancement and DWI. 

T1 postcontrast shows parenchymal enhancement as vessels recanahze Can be seen at 2-3 days, consistently seen at 6 days and persists for 6-8 weeks... 

In the subacute phase, arterial vascular enhancement peaks at 1-3 days. Large infarcts will also demonstrate meningeal enhancement that may represent reactive hyperemia, which peaks at 2-6 days. Both arterial and meningeal enhancement typically resolve by 1 week [11]. Parenchymal enhancement also occurs during this phase gray matter enhancement can appear band-like or gyriform (Fig. 6.5). This is secondary to disruption of the BBB and restored tissue perfusion from a recanalized occlusion or collateral flow. 

Parenchymal enhancement may be visible at 2-3 days, but is consistently present at 6 days and persist for 6-8 weeks [11]. Some infarcts, such as watershed and non-cortical infarcts, may enhance earlier. 

Hjort, N., et al., MRI detection of early blood-brain barrier disruption parenchymal enhancement predicts focal hemorrhagic transformation after thrombolysis. Stroke, 2008. 39(3) p. 1025-8. 

Soyer P, Dufresne AC, Somveille E, Scherrer A (1997) MR imaging of the liver effect of portal hypertension on hepatic parenchymal enhancement using a gadolinium chelate. JMRI 7 142-146... 

Comey CH, Kondziolka D, Yonas H (1997) Regional parenchymal enhancement with mixed cavernous/venous malformations of the brain case report. J Neurosurg 86 155-158... 

Seldom are renal parenchymal abnormalities consistent with RPD picked up as an incidental finding on a US, CT or MRl study performed because of a different query, such as interstitial (septic) renal involvement and parainfectious GN in a septic patient, or RPD in a dystrophic child. Contrast-enhanced CT studies may demonstrate delayed and prolonged parenchymal enhancement with reduced cortico-medullary differentiation of enlarged kidneys in acute GN. In general radiopaque intravenous contrast as administered for IVU or CT should be avoided in RPD with renal functional impairment if these studies are performed, good hydration as well as diuretic measures are compulsory to prevent possible contrast nephropathy with renal damage such as papillary necrosis or even renal failure (Erley and Bader 2000 Morcos 1998 Murphy et al. 2000). 

An arterial-portal venous shunt can be detected with helical CT or dynamic contrast-enhanced MR imaging. The findings consist of early parenchymal enhancement associated with early filling of the portal vein (Hanafusa et al. 1995). Arterio-portal shunts are found in 25% of hemangiomas. They are not related to the lesion size but they are more frequently seen in hemangiomas with rapid enhancement (Fig. 8.3) (Kim et al. 2001b). 

Fig. 7.16. Image from a 44-year-old man obtained 9 months after simultaneous pancreas-kidney transplantation with graft necrosis but without local infection or sepsis and subsequent graft extirpation. Contrast-enhanced multidetector CT shows absent parenchymal enhancement and emphysematous transformation of pancreatic graft arrow) consistent with innocuous gas collection. Annotation renal graft black asterisk) and ascites white asterisk)...

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