DX: Cystic brain metastases from lung cancer

Cystic lesions in brain have a broad spectrum. In order of frecuency, NCC is a parasitic infection common in  this lattitude so, we recommended pharmacological treatment and a new MR control when over. Patient did not resolve symptoms and control (not shown) was without change.  In efforts to a definitive diagnosis, we called the neurologist to review patient history. We found that this patient was treated years ago from lung small cell carcinoma!. He underwent chemotherapy and was in remission. He was complaining from cough and chest pain since neurological symptoms. Surprisingly, he skipped the yearly CT control in the past year. We asked for a thorax CT control. 

Here is the control wich clearly shows a left perihiliar lung mass with inflitration to thoracic wall:

With this in mind the possibility of a metastases was clear, even though cystic metastases are uncommon. Brain glioma and abscess were good differentials as well although DWI was completely normal, so abscess can be almost ruled out. We recommended a Magnetic Resonance Spectroscopy (in other institution), shown above:

Single-Voxel MRS showed increased lactate peak and reduction in NAA/Cr and Cho/Cr. Elevation in lactate are found in high-grade gliomas and metastases. Due to medical background metastases was  considered. Almost all high grade gliomas are found with elevation in NAA or Cho metabolites. In summary, although MRS can give information of the celularity of the tumor and in consecuence narrow the differentials, clinical data are mandatory in confirming the diagnosis. Patient is programmed to have a biopsy but oncologic therapy was initiated.

Detection of an intracranial mass on imaging in patients with a known primary raises the possibility of metastasis. Often the diagnosis of an intracranial metastasis is made radiologically without histological confirmation. However, radiological evaluation has its own limitation. Though the MRI has increased the specificity of diagnosis, routine MRI sequences may still not be able to differentiate between different intracranial lesions. The classical appearance of a metastasis is a solid enhancing mass with well-defined margins and extensive edema. Occasionally, central necrosis produces a ring enhancing mass. Such a lesion is difficult to differentiate from an abscess. Recently, diffusion and spectroscopy sequences have proven useful to differentiate between the two entities.

Brain metastases occur in 25%-35% of all cancer patients. The majority of brain metastases are solid tumors; cystic brain metastases are unusual. Several reports of cystic brain metastases associated with non-small cell lung carcinoma have been described, but small cell lung carcinoma presenting with cystic brain metastases is previously recognized in only one study.

This was a difficult case and I appreciate your comments. As some might have seen I'm no expert in MRS yet  :) . All comments are welcome. 

Here are some useful links, 

http://journals.lww.com/clinpulm/Abstract/2005/11000/Cystic_and_Solid_Brain_Metastases_in_a_Patient.11.aspx

http://www.bioline.org.br/request?cr10086

http://www.ajnr.org/content/32/9/1646.full.pdf+html

http://radiology.rsna.org/content/222/3/715.full.pdf+html

http://www.medscape.com/viewarticle/582031_6

http://www.cancerjournal.net/article.asp?issn=0973-1482;year=2010;volume=6;issue=3;spage=356;epage=358;aulast=Shetty