18F-FDG brain and whole body (WB) PET/CT in intracranial leptomeningeal carcinomatosis and in paraneoplastic neurologic syndromes

Background-Aim: Leptomeningeal carcinomatosis (LC) is usually
diagnosed by brain magnetic resonance (MRI) and repeated cerebrospinal fluid (CSF) analyses. Paraneoplastic neurologic syndromes
(PNS) are heterogeneous neurological disorders due to abnormal
immune system response to unknown tumor and are diagnosed by
serum specific autoantibodies (SSA), CSF, MRI and total body (WB)
computed tomography (CT). Sometimes, in both these conditions the
diagnosis is difficult. We evaluated 18F-FDG brain and WB PET/CT
usefulness in patients with clinical signs suspected for LC and PNS,
but with inconclusive or discordant CSF, SSA, MRI or CT.
Methods: We retrospectively evaluated nine consecutive patients,
five with suspected clinically signs of LC (Group A) and four with
suspected PNS (Group B). In Group A, two cases (A-B) had been
treated for breast carcinoma, two for lung adenocarcinomas (C-D) and
the remaining one for rib chondrosarcoma (E). Initial CSF cytology
was not conclusive in all patients; MRI was uncertain in A, B, C, D
cases while in case E it was not practicable because of pacemaker. In
Group B, one case had negative CSF and CT and positive SSA and MRI (F), one had positive CSF but negative SSA, MRI and CT (G),
one had positive CFS and SSA but negative MRI and CT (H) and the
remaining case had negative CSF, SSA, MRI, and CT (I). All patients
underwent both WB and brain 18F-FDG PET/CT (Discovery 710, GE
Healthcare) after i.v. 370 MBq dose.
Results: In Group A, brain PET/CT evidenced numerous hypermetabolic foci in cerebral structures suggestive for LC in four cases (A,
C, D, E). MRI remained unclear in repeated exams for intracranial
lesions, while CSF only after repeated lumbar punctures ascertained
cells with atypical mitosis suggestive for neoplastic cell dissemination
(A, C, D, E). Moreover, in case A, WB PET/CT detected an elevated
metabolic activity focus in medullary channel also evidenced by MRI
and in case C a lung focus corresponding to adenocarcinoma already
identified at diagnostic CT. However, both brain and WB PET/CT
were negative in patients B, excluding LC, as confirmed by repeated
CSF, despite unclear MRI. In Group B, brain PET/CT evidenced
hypermetabolic areas in different cortical cerebral regions in three
cases (F, G, H) which were classified as affected by PNS whose
symptoms improved after treatment excluding metastatic lesions;
however, during follow up, case H developed lung adenocarcinoma
ascertained by WB PET/CT. Brain PET/CT was negative in the
remaining one case I in whom further MRI evidenced demilinizing
plaques in the bulb and spinal cord classifying him as affected by
demyelinating disease and treated with immunosuppressant therapy.
Conclusions: In the present study, both brain and WB PET/CT
proved useful complementary diagnostic tools to ascertain LC and
PNS, and the latter also for ascertaining extra cerebral neoplastic
lesions. In particular, PET/CT is useful when MRI and CT are
uncertain or not practicable or CSF and SSA are initially inconclusive. These data need to be confirmed by a larger number of case.