Internal iliac lymph nodes
The internal iliac lymph nodes (often shortened to internal iliac nodes) are the lymph nodes found adjacent to the internal iliac artery and its branches and drain the regions supplied by these vessels. This encompasses a large area from the genitalia anteriorly, the psoas muscle posteriorly and medial thigh inferiorly (see internal iliac artery for discussion of branches). The internal iliac lymph nodes lie posterior to the external iliac lymph nodes and can be split into four groups:
- anterior group: anterior to anterior branch of the internal iliac artery
- lateral sacral group: adjacent to the lateral sacral artery
- presacral group: anterior to the sacrum
- hypogastric group
The hypogastric lymph nodes have been used in two different ways. Some authors use them synonymously with all the internal iliac nodes, whilst others restrict the term to the most superior subgroup . Historically the internal iliac artery was also known as the hypogastric artery.
The Terminologia Anatomica (TA) states that the term hypogastric nodes as a synonym for the internal iliac nodes should be abandoned, despite which this historical usage persists .
Although spread to the external iliac nodes in malignancy occurs more frequently than the internal iliac nodes, some studies have demonstrated the incidence to be twice as high , the internal iliac lymph nodes are amongst the first nodes that malignancies within the pelvis spread to along with external iliac nodes. It is far more likely to see positive nodes in these areas than in the common iliac or para-aortic regions that are more proximal, and it is rare to have proximal positive nodes in the absence of nodes distally .
Under normal circumstances, it can be difficult to identify internal iliac nodes using CT/MRI as they are often too small. Enlarged nodes with a diameter of 10 mm or more along their shortest axis are deemed to be positive (in patients with malignancy), those with a diameter of between 5 and 10 mm are deemed to be suspicious .