Leptomeningeal carcinomatosis as only pathological finding at FDG-PET/CT in case of tumor marker elevation in breast cancer

Leptomeningeal carcinomatosis (LC) is a rare and devastating disease consists of cerebral spinal fluid dissemination of malignancy with invasion into the meninges. Although the prognosis is poor with patient survival of several months, early diagnosis is important in order to relieve symptoms, improve or stabilize the neurologic status, and prolong survival with the treatment.[12]

We present a 47-year-old female patient with a history of invasive ductal carcinoma of the breast, who had been treated with mastectomy, axillary nodal evacuation, hormone therapy and locoregional radiotherapy. Three years after the achievement of complete remission, the patient presented a progressive elevation of serum tumor marker CA 15-3 (68.3 U/ml, range < 28). A thoracoabdominal computerized tomography (CT), Tc-99m bone scan and an F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT were performed, but there was no evidence of recurrence or metastases. Nine months later CA 15-3 still remained raised (49.3 U/ml, range < 28) and after a week of moderate sciatica pain, an FDG-PET/CT study was repeated to evaluate for recurrent disease. It was performed 60 min after the intravenous injection of 281 MBq (7.6 mCi) F-18 FDG, subsequent to a 6-h fast with a whole body full ring PET/CT camera (Discovery LS GE, USA). The only finding was an abnormal FDG accumulation at the vertebral foramen at thoracic and lumbosacral regions. These FDG avid lesions were located at the level of T2 vertebra (maximum standardized uptake value [SUVmax] 3.0), T6 (SUVmax 5.8), T8 (SUVmax 3.0) [Figure 1a], T11 (SUVmax 2.1), L5 (SUVmax 2.5) and at the level of sacrum (SUVmax 4.1) [Figure 1b], suggesting diffuse leptomeningeal metastasis. The patient was referred for gadolinium contrast spinal MRI and it showed enhancing linear and nodular thickening on the cord surface [Figure 1c] highly suggestive of LC. Cytological examination of the cerebrospinal fluid was performed, and it was reported as positive for malignant cells, confirming the diagnosis of LC.

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Figure 1 (a) Sagittal PET and fused PET/CT images showing pathological FDG uptake at the level of T2 vertebra (thin arrow), T6 (thick arrow) and T8 (dotted arrow). (b) Focal area of uptake at the level of sacrum (arrow) at the sagittal PET and fused PET/CT images. (c) Sagittal slice of gadolinium contrast spinal MRI showing linear (thin arrows) and nodular (thick arrow) leptomeningeal enhancement over the posterior surface of the spinal cord.

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About 2-5% of patients with breast cancer may develop LC,[3] being the most common solid tumor to exhibit leptomeningeal colonization.[4] It is common for most patients to have intraparenchymal brain metastases concurrent with LC[5] and widely disseminated cancer. MRI is very useful for the diagnosis of LC, but it is almost always performed when the patient is symptomatic. Occasionally, as the case we present, leptomeningeal metastasis can be the only site of distant recurrence.[6] As clinical signs and symptoms of LC may be absent or may underestimate the extent of macroscopic disease,[1] so when performing a FDG-PET/CT to look for distant metastatic sites, close attention should be paid to the entire spinal canal, since these lesions can easily be mistaken for physiologic uptake.