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Neuroradiology Case of the Week

Case 341

August 2008

Harshabad Singh,MBBS,Taik-Kun Kim, MD,
and P-L Westesson,MD, PhD, DDS

Clinical Presentation: Patient is a 57-year-old male with metastatic lung cancer who presents with new onset of mental status changes. There is clinical concern for brain metastases.

Imaging Findings: MR Imaging is the most sensitive test to detect hematogenously disseminated metastasis. MR imaging revealed two masses with typical imaging features of metastasis. Perfusion MRI showed areas of intense increase in rCBV which is another feature of metastasis.

Diagnosis: Metastatic lung cancer that demonstrates increased perfusion on MR Imaging

Discussion: Metastases represent 40% of the intracranial neoplasms .Lung and breast are the most common primary sites. Melanoma, renal cell and thyroid also commonly metastasize intracranially [1].
     On T1WI, most metastases are hypointense surrounded by more hypointense perilesional edema and are characteristically located at the gray white matter junction. Metastases enhance on contrast administration. T2WI is sensitive to perifocal white matter edema that surrounds the metastasis. On this sequence the solid portion is generally of low intensity unless it has blood products, melanin or is necrotic. Necrotic lesions are hyperintense on T2WI, whereas melanin is hypointense. The appearance of blood products depends on the state they are in [2].
     Newer MR imaging techniques like perfusion MR imaging provide information in addition to that obtained from conventional MR imaging and are helpful in grading gliomas, differentiating various tumors and distinguishing tumors from non-neoplastic lesions.
Perfusion-weighted imaging provides information about tumor tissue perfusion. The standard measurement used is relative cerebral blood volume (rCBV; i.e. cerebral blood volume relative to contralateral white matter). This has been shown to correlate with microvessel density. Higher microvessel density is usually found in high-grade malignant tumors. Increased tumor vascularity however is not synonymous with malignancy. Some tumors like choroid plexus papillomas and meningiomas can be highly vascular but display benign biologic behavior. Pattern of tumor enhancement on conventional MR imaging is not always reliable to obtain precise information about tumor angiogenesis at the capillary level, as enhancement is mainly due to the disruption of blood-brain barrier (BBB) rather than the tumoral vascular proliferation itself. But when the BBB is severely disrupted, perfusion MR may show a falsely low rCBV due to leakage of contrast which causes unwanted T1 effects that counteract the T2-signal lowering effects of gadolinium [3-5].
     Peritumoral rCBV is being used to differentiate solitary metastases from gliomas. Metastasis have decreased peritumoral rCBV as compared from gliomas. Most parenchymal metastases have well-defined borders surrounded by pure vasogenic edema whereas high-grade gliomas have peritumoral infiltration which accounts for the increased perfusion in these regions [6]. In this particular case the areas of increased perfusion are clearly demarcated from the surrounding brain parenchyma which favors a metastatic lesion. Perfusion-weighted imaging may be useful in determining the likely origin of cerebral metastasis in a patient with an unknown primary, although more definitive studies are needed. The mean maximum rCBVs of melanoma and renal carcinoma metastases are significantly greater than those of high-grade gliomas, but there was no significant difference between high-grade gliomas and lung metastases [3].
     With the development of anti-angiogenic treatment, perfusion imaging may help assess response and hence the efficacy of the treatment [6].

References:

1. Bragg D, Rubin P, Hricak H. Oncologic Imaging, 2nd ed. WB Saunders Co, 2002: 149.
2. Zimmerman RA, Gibby WA, Carmody RF. Neuroimaging: Clinical& Physical Principles. 1st Ed., Springer Verlag Inc. 2000: 1023-1024.
3. Rees J. Advances in magnetic resonance imaging of brain tumours. Curr Opin Neurol. 2003 Dec;16(6):643-50. [Pub Med]
4. Bulakbasi N, Kocaoglu M, Farzaliyev A, Tayfun C, Ucoz T, Somuncu I. Assessment of diagnostic accuracy of perfusion MR imaging in primary and metastatic solitary malignant brain tumors. AJNR Am J Neuroradiol. 2005 Oct;26(9):2187-99. [PubMed]
5. Cho SK, Na DG, Ryoo JW, Roh HG, Moon CH, Byun HS, Kim JH. Perfusion MR imaging: clinical utility for the differential diagnosis of various brain tumors. Korean J Radiol. 2002 Jul-Sep;3(3):171-9. [PubMed]
6. Cha S. Perfusion MR imaging of brain tumors. Top Magn Reson Imaging. 2004 Oct;15(5):279-89. [PubMed]