Grading of Anal Mass
Grading of an anal mass is primarily accomplished through clinical examination and histopathological assessment of biopsy specimens, with T-stage determined by physical examination measuring tumor size and N-stage assessed through imaging and tissue sampling of suspicious lymph nodes. 1
Clinical Staging Approach
Primary Tumor Assessment (T-Stage)
T-stage is primarily determined through clinical examination rather than imaging. 1 The essential components include:
- Digital rectal examination (DRE) to assess tumor size, location, and relationship to sphincter complex 1
- Anoscopic examination to visualize the lesion directly 1
- Examination under anesthesia (EUA) when the lesion is painful or when precise measurements are critical for treatment planning—ideally with the radiation oncologist present to document exact measurements 1
- Vaginal examination in women (particularly for low anterior tumors) to assess vaginal/vaginal septal involvement and potential fistula formation 1
Nodal Assessment (N-Stage)
Lymph node evaluation requires both clinical palpation and imaging, with tissue confirmation for enlarged nodes. 1
- Palpation of inguinal lymph nodes, focusing on superficial inguinal nodes medial and close to the pubis 1
- Fine-needle aspiration (FNA) and/or excisional biopsy of clinically or radiologically enlarged nodes (>10 mm on CT/MRI) 1
- CT or MRI of the pelvis to evaluate pelvic lymph nodes and assess involvement of other abdominal/pelvic organs 1
Imaging for Staging
MRI of the pelvis is the preferred imaging modality for local staging, providing superior soft tissue contrast and spatial resolution. 1
- High-resolution T2-weighted MRI provides information on tumor size, local extent, invasion of adjacent organs, and more accurate nodal assessment 1
- Endoanal ultrasound (EUS) offers excellent spatial detail for tumor size and depth of mural invasion but is best reserved for small T1 lesions due to limited field-of-view 1
Distant Metastasis Evaluation (M-Stage)
- CT chest to evaluate for pulmonary metastases, as anal veins drain into systemic circulation 1
- CT abdomen to assess possible disease dissemination 1
Role of PET/CT
PET/CT can be considered to verify staging before treatment, particularly for detecting lymph node involvement. 1
- PET/CT has high sensitivity (93%) for detecting lymph node involvement but lower specificity (76%) 1
- PET/CT changes nodal status in 21% and TNM stage in 41% of patients 1
- The main impact is identifying metabolically active lymph nodes and influencing radiation therapy planning 1
- However, PET/CT is not a replacement for diagnostic CT and routine use for staging has not been fully validated 1
Critical Pitfalls to Avoid
Small pelvic nodal metastases (<0.5 cm) are often missed on routine CT and PET imaging, as demonstrated in surgical series 1. This means clinical staging may underestimate nodal involvement.
Enlarged inguinal nodes are frequently reactive rather than metastatic (30-50% of palpable inguinal lymphadenopathy is inflammatory) 2, making tissue confirmation essential before treatment decisions.
Do not confuse anal squamous cell carcinoma with rectal adenocarcinoma—they are indistinguishable on MRI, so biopsy confirmation before imaging is mandatory to determine appropriate staging system and treatment 3, 4.