Intracerebral metastases other imaging findings

Other imaging tests for intracerebral metastases include magnetic resonance spectroscopy (intratumoural choline and lipid peak with depleted N-acetylaspartate), magnetic resonance perfusion (reduced cerebral blood volume and cerebral blood flow in the region of metastasis), and positron emission tomography (hypermetabolic, hypometabolic, or variable metabolism depending on the primary).^[1][2]

• MR spectroscopy may be helpful in the diagnosis of intracerebral metastases.^[1]
• Findings on MR spectroscopy include:^[1]

• Intratumoral choline peak with no choline elevation in the peritumoral edema
• Any tumor necrosis results in a lipid peak
• N-acetylaspartate (NAA) depleted

• MR perfusion demonstrates reduced CBV (cerebral blood volume) and CBF (cerebral blood flow) in the region of metastasis. Surrounding edema demonstrates normal CBV.^[3]

• 
  _{MR perfusion of brain of a known case of renal cell carcinoma demonstrates reduced CBV (cerebral blood volume) and CBF (cerebral blood flow) in the region of metastasis. Surrounding edema demonstrates normal CBV.^[4]}
• 
  _{MR perfusion of brain of a case of renal cell carcinoma demonstrates highly variable appearance of hemorrhagic metastases to the brain.^[4]}

1. Fludeoxyglucose F 18-positron emission tomography (FDG-PET)

• Fludeoxyglucose F 18-positron emission tomography is generally considered as the best imaging tool for metastases.^[2]
• However, it can only detect metastases upto 1.5 cm in size, therefore contrast MRI remains the gold standard to rule out small metastases. Lung, breast, colorectal, head and neck, melanoma, and thyroid metastases are usually hypermetabolic.
• Mucinous adenocarcinoma and renal cell carcinoma are typically hypometabolic.
• Gliomas and lymphomas are variable.
• Any central hypometabolism indicates necrosis.

2. Positron emission tomography/computed tomography (PET/CT)

• PET/CT may have higher sensitivity in detecting metastases, partly due to hybrid imaging part, computed tomography (CT).
• It may even demonstrate asymptomatic metastases in patients examined for extracranial disease.

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