Inguinal Lymph Node Assessment: 16mm Short Axis, 27mm Long Axis with Preserved Fatty Hilum
This lymph node requires further evaluation with fine-needle aspiration (FNA) or excisional biopsy, as both the short axis (16mm) and long axis (27mm) exceed established thresholds for abnormality, despite the reassuring presence of a preserved fatty hilum. 1
Size Threshold Analysis
The dimensions of this lymph node are clinically significant:
The 16mm short axis exceeds multiple established cutoffs: The American College of Radiology uses 10mm as the threshold for superficial inguinal lymph node metastases in vulvar cancer staging, and this node is 60% larger than that threshold 1. The general ACR recommendation for inguinal nodes requiring further evaluation is >15mm short axis, which this node exceeds 1.
The 27mm long axis is also abnormal: Normal inguinal lymph nodes have a maximum long axis of 21mm, making this node 29% larger than the upper limit of normal 1. This measurement exceeds the 20mm threshold used in multiple oncologic staging systems 1.
In the context of penile cancer specifically: The National Comprehensive Cancer Network defines N1 disease as lymph node mass ≤20mm, while N2 disease is >20mm but ≤50mm, placing this 27mm node in the N2 category 1.
Morphologic Features: The Fatty Hilum Paradox
While the preserved fatty hilum is a reassuring feature, it does not exclude malignancy in this size range:
Most benign nodes demonstrate a central fatty hilum, smooth borders, and homogeneous attenuation 2. The presence of these features generally suggests benignity 2.
However, size trumps morphology at these dimensions: When both short and long axis measurements independently exceed abnormality thresholds, the preserved fatty hilum becomes less reliable as a negative predictor 1.
The long-to-short axis ratio is 1.69:1 (27÷16), which is above the suspicious threshold of <1.3:1 used in vulvar cancer imaging 2, 1. However, this ratio falls into an indeterminate zone where size criteria become more important than morphologic features 1.
Recommended Management Algorithm
Given the family history of cancer and the size parameters, proceed as follows:
Step 1: Fine-Needle Aspiration (FNA)
- For palpable inguinal lymph nodes <40mm, FNA is the recommended initial diagnostic approach 2, 1.
- US-guided FNA is preferred for accuracy and has 86% sensitivity and 96% specificity when combined with ultrasound assessment 2.
Step 2: If FNA is Negative
- Proceed to excisional biopsy, as FNA can miss micrometastases 2.
- The minimally invasive nature of FNA justifies this two-step approach despite potential undersampling 2.
Step 3: If FNA is Positive
- Complete inguinofemoral lymphadenectomy is indicated rather than sentinel lymph node biopsy alone 1.
- Nodes >15mm short axis warrant complete lymphadenectomy in oncologic contexts 1.
Step 4: Cross-Sectional Imaging
- CT or MRI should be performed to assess extent, location, and relationship to surrounding structures 1.
- This is particularly important given the family history of cancer and to evaluate for additional nodal disease 1.
Critical Caveats
Do not assume malignancy based on size alone: 30-50% of palpable inguinal lymphadenopathy is inflammatory rather than malignant 1. Tissue diagnosis is essential before proceeding to definitive surgical management 1.
Clinical context dramatically alters pretest probability: The presence of a primary malignancy, skin lesions on the lower extremity, or constitutional symptoms changes management urgency 1. The family history of cancer increases suspicion but does not establish diagnosis 1.
Avoid sentinel lymph node biopsy as the sole diagnostic approach: Given these dimensions, if malignancy is confirmed, complete lymphadenectomy is required rather than sentinel node sampling alone 2, 1. Dynamic sentinel node biopsy has shown disappointing results with sensitivity of only 71-80% and false-negative rates of 18% 2.