Assessing Nodal Activity in Non-Lymphoma Cases
[Assessing nodal activity in lymphoma cases is addressed in detail, here.]
For most primary malignancies, PET/CT can be a powerful tool in the assessment of regional and distant metastatic adenopathy.
There are 2 main challenges the PET/CT radiologist must address when assessing FDG-avid lymph nodes:
- Is an FDG-avid lymph node metastatic or reactive/inflammatory?
- Is a small (< 8.0 mm) non-avid or minimally avid node – one considered “beneath the resolution of PET ” – malignant?
Because each case must assessed in the clinical context of its specific presentation (“oncologic plausibility”, discussed here), there are no hard and fast rules for determining whether an FDG-avid node is metastatic or inflammatory/reactive.
At PETCTMD, we generally approach FDG-avid nodes by asking 3 central questions, and then applying the following algorithm:
Question #1: Is it reasonable to expect a metastatic lymph node in this location?
Question #2: Is there a clinical explanation for an otherwise suspicious node to be considered reactive/inflammatory?
Question #3: Does a clinically suspicious, but not significantly FDG-avid, node measure less than 8.0 mm?
Case 1
Case 1 (Image 2)
If an FDG-avid left axillary node would be a reasonable site for metastatic disease — in the clinical context of this specific patient — then it is highly suspicious for a metastasis. If, however, a solitary metastasis to the left axilla would be nearly incredulous, then it is highly likely to be reactive/inflammatory and follow up can be obtained.
Case 2
Case 2 (Image 2)
Patient presents for initial staging of left breast cancer, intensely avid (red arrow). A tiny FDG-avid left internal mammary lymph node is present (white arrow). Despite its extremely small size (which would not raise an eyebrow if this was only a CT scan), it metabolic activity greater than liver uptake is consistent with metastatic adenopathy.
Case 2 (Image 3)
A solitary enlarged retroperitoneal lymph node is present in this patient presenting for re-staging of a colon cancer (with rising tumor markers). Its metabolic activity greater than liver uptake is consistent with metastatic disease.
Case 2 (Image 4)
A solitary enlarged retroperitoneal lymph node is present in this patient presenting for re-staging of testicular cancer. Its metabolic activity greater than liver uptake is consistent with metastatic disease.
Case 2 (Image 5)
A solitary FDG-avid left inguinal lymph node (white circle) is present in this patient presenting for initial staging of a prostate cancer (red circle). Its metabolic activity greater than liver uptake is consistent with metastatic disease.
Case 2 (Image 6)
A solitary FDG-avid right cervical lymph node (white circle) is present in this patient presenting for initial staging of a right tonsillar cancer (red arrows). Its metabolic activity greater than liver uptake is consistent with metastatic adenopathy.
Case 3
Case 3 (Image 2)
Patient presents for follow up of a thyroid carcinoma. A minimally prominent left cervical lymph node is present, mildly FDG-avid. As its metabolic activity is less than liver uptake, it is considered a benign reactive/inflammatory lymph node. Some radiologists will recommend a follow up study for this node, if its metabolic activity is greater than mediastinal blood pool uptake.
Case 3 (Image 3)
A mildly prominent anterior mediastinal node is present in this patient previously treated with chemotherapy for metastatic testicular cancer. As its metabolic activity is less than liver uptake, it is considered a benign finding, presumably representing treated disease. Unfortunately, the patient’s prior studies were performed in another country and were unavailable for comparison.
Case 3 (Image 4)
A mildly prominent left mediastinal lymph node is present in this patient presenting for initial staging of melanoma. As its metabolic activity is less than liver uptake, it is considered a benign reactive/inflammatory lymph node.
Case 4
Case 4 (Image 2)
Patient presents for initial staging of rectal cancer. A 4.0 mm (short axis) left perirectal lymph node is present. Although non-avid, its size is beneath the resolution of PET. Therefore, this node must be considered indeterminate (this node was positive at surgery).
Case 4 (Image 3)
Patient presents for initial staging of rectal cancer. A 5.0 mm (short axis) left perirectal lymph node is present. Although non-avid, its size is beneath the resolution of PET. Therefore, this node must be considered indeterminate (this node was negative at surgery).
Case 4 (Image 4)
Patient presents for initial staging of rectal cancer. A 6.0 mm (short axis) right perirectal lymph node is present, mildly FDG-avid. As its size is beneath the resolution of PET, its metabolic activity is very likely underestimated. Therefore, even mild metabolic activity in a node of this size is suspicious for metastatic disease (this node was positive at surgery).
Case 4 (Image 5)
Patient presents for initial staging of rectal cancer. A 7.0 mm (short axis) perirectal lymph node is present, mildly FDG-avid. As its size is beneath the resolution of PET, its metabolic activity is very likely underestimated. Therefore, even mild metabolic activity in a node of this size is suspicious for metastatic disease (this node was negative at surgery).