High fluorodeoxyglucose (¹⁸F)PET-uptake lymph nodes in a patient with chordoma: Tumor metastasis or sarcoidosis?

Background

FDG-PET has been used for diagnosis and staging of different malignancies including chordoma [1]. Chordoma is rare, highly recurrent, locally aggressive malignant tumor, originating from remnants of notochord. Metastases without local recurrence of primary neoplasm are extremely rare and most frequently seen at lungs (48%), bones (26%) and liver. Sporadic cases of metastases to CNS, lymphatic organs and skin have been reported [2]. Here, we report a rare case of 48-year-old Caucasian man with recurrent chordoma and lymph node involvement by sarcoidosis, which mimicked appearance of metastatic disease in PET-CT, scan.

Case Report

A 48-year-old man with a history of surgical resection for sacral chordoma in March 2011, presented to the clinic with recurrent sacrococcygeal pain in June 2012. Lumbosacral MRI was performed and showed a 0.5×0.8×1.0 cm, T2 hyper intense lesion, located in sacrococcygeal region, which was consistent with recurrent chordoma (Figure 1).

Therefore, patient underwent a whole body PET-CT scan for staging. On PET-CT scan FDG avid lymph nodes in the left external iliac and bilateral femoral chains were detected (Figure 2).This raised the suspicions for a tumor metastasis to adjacent lymph nodes. The patient underwent open lymph node biopsy with pathology that unexpectedly revealed noncaseating epithelioid granuloma without evidence for malignant cells (Figure 3).

The patient underwent an en-bloc resection of soft tissue of the buttocks and peri-rectal region, with distal sacrectomy (S4–5). The surgical specimen pathology showed chordoma cells in the bone and further non-caseating epithelioid granulomas in the bone marrow consistent with diffuse sarcoidosis (Figure 4).

Discussion

Two cases have been reported in the literature in which malignant tumor was accompanying by high FDG-uptake sarcoidosis lesions. The first was primary rectal cancer and accompanying high FDG-uptake sarcoidosis lesions in the bone [3], and the second was primary carcinoid tumor of the lung coincident with high FDG-uptake sarcoidosis of the bone marrow [4]. However, coincidence of chordoma and sarcoidosis has not yet been reported in the literature.

Sarcoidosis can be intensely FDG avid in PET scan, and thus, it may mimic the diagnosis of metastatic neoplastic disease. Combination of FDG-PET and FMT-PET(fluorine methyl tyrosine) scanning [5] or dual time point FDG-PET imaging [6] are reported as promising techniques in differentiating malignant from benign inflammatory diseases such as sarcoidosis.

Conclusions

Lymph node involvement in sarcoidosis is rare but can lead to false-positive appearance of metastatic disease in PET-CT scan.