Anal Cancer
Fast Facts:
- 2% of GI malignancies (1:500 lifetime risk)
- Female > Male
- High association with HPV
- Increasing incidence over the past 30 years
- 80% squamous cell carcinoma (20% adenocarcinoma)
- Localized Disease 5-year survival: ≈ 80%
- Distant Disease 5-year survival: ≈ 30%
Treatment:
- Standard of care for anal cancer is radiochemotherapy.
- Surgery reserved for persistent or recurrent disease.
Indications for PET/CT Imaging:
Initial Staging: Permits both assessment of initial disease and serves as a baseline exam for follow up reference.
- Pre-therapy imaging changes management in 20-33% of patients.
- Prognosis: The higher the SUV of the primary, the poorer patient survival.
- PET/CT scan used for radiation therapy treatment planning.
- Primary lesion: Size, location and metabolic activity (very often, the lesion will only be seen on the PET images).
- Regional Nodal Status: High sensitivity for lesions ≥ 8.0 mm.
- Distant Metastatic Disease: Most commonly to the liver, lungs and bone.
Assessing Response to Therapy & Prognosis:
- Early Response: Non-responders can be offered alternative therapy.
- Late Response: Assess success or failure of therapy, and ultimate outcome.
Recurrence & Restaging:
- PET/CT is utilized for patients with known or suspected recurrent disease (or at high risk for recurrence).
- Distinguishing recurrence from post-therapeutic inflammation/scarring.
False Positive:
- Hemorrhoids: Hemorrhoidal inflammation is an extremely common cause of focal increased uptake in the ano-rectal region. For this reason, it is extremely rare to incidentally diagnose an anal cancer on PET/CT (it is simply unacceptable to raise a question of anal cancer in every patient with probable hemorrhoidal inflammation).
Case 1
Case 1 (Image 2)
Axial fused image demonstrates a focus of intense FDG uptake in the ano-rectal region. The co-registered CT image does not clearly demonstrate an associated soft tissue mass. Unfortunately, most small anal cancers are not clearly identifiable on non-contrast CT images.
Case 1 (Image 3)
Sagittal fused image demonstrates a focus of intense FDG uptake in the ano-rectal region. If we were not given the history of a newly diagnosed anal cancer, we would presume such uptake to represent hemorrhoidal inflammation (discussed in detail, here).
Case 2
Case 2 (Image 2)
Axial fused image demonstrates a focus of intense FDG uptake in the ano-rectal region, consistent with the patient’s diagnosis of anal cancer. Ill-defined FDG-avid stranding within the subcutaneous fat of the right gluteal region is present, consistent with a recent subcutaneous injection of medication.
Case 2 (Image 3)
Intensely avid left inguinal lymph node, suspicious for metastatic disease.
Case 3
Case 3 (Image 2)
Axial images demonstrate the patient’s large hypermetabolic anal cancer. While the non-contract CT images often fails to delineate small anal cancers, this large soft tissue mass is easily seen on the CT images.
Case 3 (Image 3)
FDG-avid right perirectal lymph node. Although only moderately avid, it measures only 7.0 mm, which is considered “beneath the resolution of PET”. Its small size very likely underestimates its true metabolic activity. This small node is highly suspicious for metastatic adenopathy.
Case 4
Case 4 (Image 2)
Axial fused image demonstrates intense uptake in the ano-rectal region, consistent with the patient’s reported history of a newly diagnosed anal cancer. The non-contract CT images fail to demonstrate a corresponding soft tissue lesion.
Case 4 (Image 3)
Three small perirectal lymph nodes. Although only mildly avid, these measure less than 8.0 mm, considered “beneath the resolution of PET”. Their small size very likely underestimates their true metabolic activity. These small nodes are suspicious for metastatic adenopathy.
Case 5
Case 5 (Image 2)
Axial fused image demonstrates intense uptake in the ano-rectal region, consistent with the patient’s reported history of a newly diagnosed anal cancer. The non-contract CT images fail to clearly demonstrate a corresponding soft tissue lesion.
Case 5 (Image 3)
MIP from a 6-month follow up scan suggests interval development of FDG metastatic disease to the chest and right abdomen (red arrow). Bilateral obstructive uropathy is also now suggested.
Case 5 (Image 4)
New intensely FDG-avid metastatic adenopathy to the right hilum.
Case 5 (Image 5)
New intensely FDG-avid metastasis to the right lobe of the liver.
Case 5 (Image 6)
Two new subcentimeter left lung nodules. Although non-avid, their size is beneath the resolution of PET. Their interval development since the prior exam is suspicious for metastatic disease.
Case 6
Case 6 (Image 2)
Axial fused image demonstrates intense uptake in the ano-rectal region, presumed to represent hemorrhoidal inflammation (no associated soft tissue abnormality on the co-registered non-contrast CT image).
Case 6 (Image 3)
Sagittal fused image demonstrates intense uptake in the ano-rectal region, presumed to represent hemorrhoidal inflammation (no associated soft tissue abnormality on the co-registered non-contrast CT image).
Case 6 (Image 5)
Note the relationship of the coccyx to the rectum and to the ano-rectal region.
Case 7
Case 7 (Image 2)
Axial fused image demonstrates the intense ano-rectal uptake to be located eccentric to the left. As FDG-avid hemorrhoidal inflammation is typically centrally located, direct visualization was recommended. This was a rectal cancer at the ano-rectal junction.
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