11C-methionine PET imaging of leptomeningeal metastases from primary breast cancer--a case report.

Leptomeningeal metastases (LM) is often an elusive disease frequently diagnosed at an advanced clinical stage. Early diagnosis may allow for prompt initiation of treatment with minimal tumor burden and maximal chance of survival, especially in solid tumors such as breast cancer. Although the method of choice for imaging LM currently is by gadolinium enhanced magnetic resonance imaging (MRI), the technique has a high sensitivity but low specificity. We report the first case of Carbon 11-labelled methionine (Cmet) positron emission tomography (PET) imaging of leptomeningeal metastases in a patient with primary breast cancer. This patient presented with clinical features suggestive of LM, but had inconclusive cerebrospinal fluid (CSF) findings. Although, the contrast enhanced MRI revealed calvarial and meningeal lesions, it is known that meningeal enhancement on MRI does not always indicate metastases. In this clinical dilemma the strong methionine uptake on PET helped steer the diagnosis in favor of cancerous infiltration even before the CSF cytology became positive for malignancy.