Another “great mimicker”: FDG-PET/CT imaging findings of sarcoid-like reaction

Sarcoid-like reaction (SLR) is a cause of non-caseating granulomas in some of the cancer patients with otherwise no signs or symptoms of sarcoidosis. SLR has been described in a variety of solid organ malignancies, including breast and lung cancer. SLR may result in hypermetabolic activity in 18-fludeoxyglucose positron emission tomography (PET)/CT scan, resulting in false positive reporting for malignancy. The purpose of this case series is to expose residents/practising physicians who interpret PET/CT to a series of cases illustrating findings of SLR.


Case 1
The patient was a 63-year-old male with adenocarcinoma of the rectosigmoid junction and multifocal tubular adenoma of the right colon. The patient underwent right hemicolectomy and 6 cycles of folinic acid (also called leucovorin, FA or calcium folinate)/fluorouracil (5FU) /oxaliplatin (FOLFOX).
Findings: Post-therapy positron emission tomography (PET)/CT scan showed bilateral symmetric hilar and mediastinal enlarged lymph nodes with increased 18-fludeoxyglucose (FDG) activity ( Figure 1). The maximum standardized uptake value (SUV max) of the subcarinal lymph node was 11.7, SUV max of the right hilar lymph nodes was 10.6 and that of the left hilar lymph nodes was 9. There were no lung abnormalities to suggest active infection or inflammation. Biopsy of one of these lymph nodes was consistent with sarcoid-like reaction (SLR).

Case 2
The patient was a 45-year-old female with multifocal multicentric left breast cancer, mcT2N0M0, Stage 2A, oestrogen receptor/progesterone receptor+, human epidermal growth factor 2(À). The patient had chemotherapy followed by left mastectomy and reduction of the right breast. She completed radiation therapy afterwards and started chemotherapy.  Findings: PET/CT scan after completion of radiation therapy revealed hypermetabolic symmetric hilar lymph nodes ( Figure 2). SUV max of the right hilar lymph nodes was 8.6 and SUV max of the left hilar lymph nodes was 8.5. There were no lung findings to suggest active infection. Upon review of the history with the patient's oncologist, this appearance was accepted as most consistent with SLR. Follow-up PET/CT scan revealed interval resolution of hypermetabolic lymph nodes ( Figure 3).

Case 3
A 57-year-old male with non-Hodgkin's lymphoma presented initially with a left lower extremity swelling. The patient was found to have a large mass in the left iliac wing and was diagnosed with diffuse B-cell lymphoma. The patient underwent 6 cycles of rituximab and Cytoxan (cyclophosphamide)/Adriamycin (hydroxy doxorubicin)/vincristine (Oncovin)/prednisone (also known as CHOP).
Findings: Initial PET/CT showed a lytic hypermetabolic mass in the left iliac wing with left pelvic hypermetabolic adenopathy ( Figure 4). Biopsy of the bone lesion revealed diffuse B-cell lymphoma. The first post-treatment PET/CT scan performed 8 months after completion of therapy showed a complete "metabolic" response ( Figure 5). The second follow-up PET/CT scan 2 years after completion of therapy demonstrated new mediastinal/hilar hypermetabolic adenopathy ( Figure 6). SUV max of the precarinal lymphadenopathy was 18.7, subcarinal lymphadenopathy was 26.3 and that of the right hilar lymph nodes was 24.6. Biopsy of one of these lymph nodes revealed non-caseating granulomatous inflammation. The third followup PET/CT scan after 2 years showed new abdominal hypermetabolic adenopathy (Figure 7) with SUV max of 8.7. The last follow-up PET/CT performed 2 years after the third follow-up PET/CT scan showed almost complete improvement of these findings (Figure 8). The patient did not receive any therapy after the first follow-up PET/CT scan. The second to last follow-up PET/CTs were acquired to monitor SLR-related findings. There was spontaneous resolution of FDG activity of these nodes, thus it was not a treatment-induced tumour response.

DISCUSSION
Pathophysiology of SLR is not completely understood. There are, in general, two forms, localized (around the tumour) and general (distant sites from primary tumour). The localized form of SLR could be from degenerative/necrotic changes within the  There are a variety of uptake patterns at PET/CT. The most common patterns are mediastinal nodal and/or symmetric hilar uptake. Other presentation patterns include pulmonary abnormalities, such as pulmonary nodules, ground-glass opacities, regional lymph nodes, liver, spleen or bone marrow uptake.  Case review: PET/CT findings of sarcoid-like reaction