Differential diagnosis
· Hypervascular hepatic metastasis from renal cell carcinoma
· Hepatocellualr carcinoma (HCC)
· Hypervascular benign lesion
Clue for the diagnosis:
· Because renal cell carcinoma is a hypervascular tumor and its metastasis is following its nature, i.e. hypervascular, therefore, the 1st diagnosis is metastasis , but we have to differentiate between the behavior of hypervascular malignant lesions in the liver ( metastasis and HCC ) and the other hypervascular benign lesions that can coexist incidantely ( like hemangioma, focal nodular hyperplasia and adenoma).
· The hypervascular malignant tumors in the liver are washing out the contrast in the portovenous and delayed phase more than the normal liver parenchyma (become more hypodense than the adjacent normal enhancing liver parenchyma)
· In this case, the tumour is markedly enhancing in the arterial phase, but becomes isodense to the liver parenchyma in portovenous and delayed phases, suggests a benign hypervascular tumor rather than malignant metastatic deposit.
· The tumor also has a central hypodense scar (blue arrow) which does not enhance in the arterial, or the port venous phase, but enhances in the delayed phase. The enhancement pattern of the scar is pathognomonic for focal nodular hyperplasia (FNH). The scar of FNH is formed histologically of fibrous tissue and AVM ( arteriovenous malformation) which explains its enhancement in the delayed phase ( fibrosis and AVM usually show delayed enhancement).
· The diagnosis was confirmed by sulphur colloid scanwhich showed increase uptake by the tumor which is also another pathognomonic feature of focal nodular hyperplasia as it is the only tumor that contains Kupffer cells which cause increase uptake.
· N.B.:
Multiphase contrast CT is crucial for diagnosis of any focal liver lesion (s). It is of note that this lesion was missed in a previous CT exam as it was performed as single phase contrast study.
Diagnosis :
Focal nodular hyperplasia in a patient with a history of renal cell carcinoma.
Teaching points
Focal nodular hyperplasia :
· The 2nd mostcommon benign tumor of liver after hemangioma
· Usually solitary (95%)
· Frequently has central fibrous scar contains arteriovenous malformation
· M:F= 1:4
· Highly vascular tumor
· On US: iso to hypoechoic , with displacement of hepatic vessels
· On CT :
- Transient intense hyperdensity on arterial phase, followed rapidly by isodensity on portovenous phase
- Hypodense central scar in arterial and portovenous phases , shows enhancement on the delayed phase
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· On MRI:
- Dynamic MRI has widely replaced CT for diagnosis of focal liver lesions in many institutions.
- Iso to hypointense on T1W, slightly hyperintense on T2W
- Dense enhancement on arterial phase, iso intense on portovenous phase
- Central scar: hypointense on T1W, hyperintense on T2W, and showed enhancement on delayed phase.
· On nuclear study :
* Sulphur colloid scan : normal uptake in 50-70%. Increase uptake in about 10% of cases but in such cases of increase uptake, it is pathognomonic, as the focal nodular hyperplasia is the only hepatic tumor that contains sufficient Kupffer cells to cause increase uptake.