Anatomy of the Inguinal Lymph Nodes

The lymph nodes in the inguinal lymphatic region are the first draining nodes for the penis, and the anatomy has been described by various authors. 1 7,18 Historically, the inguinal lymphatic region was divided into two groups, the superficial and deep lymph nodes. The superficial inguinal lymph nodes are located beneath Camper's fascia and above the fascia lata covering the muscles of the thigh. The deep inguinal nodes are located deep to the fascia lata and medial to the femoral vein. These nodes intercommunicate with each other and then drain into the pelvic nodes. From a clinical perspective, this anatomic distinction is not very useful as the superficial nodes cannot be distinguished from the deep nodes by physical examination or imaging. Daseler et al. divided the inguinal region into five sections by drawing a horizontal and vertical line through the point where the saphenous vein drains into the femoral vein with one central zone directly overlying the junction (Fig. 9.2).17 A recent lymphoscintigraphic study by Leijte et al. has shown that the majority of the first draining lymph nodes is located in Daseler's superomedial segment, although there is individual variation.19 In the same study, skip metastases (circumventing the inguinal lymphatic region) to the pelvic lymph nodes was not identified.19 Further confirming the rarity of direct pelvic drainage is a large series of 100 lymphangiographic examinations of the drainage of the penis by Cabanas in which no direct drainage to the pelvic region was found.20

Fig. 9.1 Lymphoscintigram showing bilateral drainage with bilateral nodal uptake of tracer (anterior view, left lateral view, right lateral view after 10 min and anterior view after 2 h)

Fig. 9.2 Division of inguinal region, originally described by Daseler

Following lymphatic dissemination to the groin, metastatic cells spread in a step wise pattern, with tumor cells embolizing to the pelvic lymph nodes and/or distant sites such as the lungs, bone, and para-aortic lymph nodes. Primary hematogenic spread has only been documented in squamous cell carcinoma of the sarcomatoid subtype.21

The first draining pelvic lymph nodes after inguinal dissemination are most commonly located in the external iliac chain. 1 9,22 The inguinal region is anatomically connected to the pelvic region, whereby the first node medial to the femoral vein in the inguinal canal is considered the first pelvic node, also called the node of Cloquet or node of Rosenmuller. The risk of metastatic disease beyond the groins is correlated with the number of involved inguinal lymph nodes and/or presence of extran-odal extension.4,22 The positive and negative predictive value of pelvic lymph node involvement in penile cancer, based on a tumor-positive node of Cloquet is 80% and 86%, respectively.22 In rare cases lymph nodes can be found in the suprapubic area (prepubic lymph nodes).23 It is unknown whether true crossing vessels run from one inguinal region to the other through these suprapubic nodes.

Cross-over from one pelvic region to the other or cross-over from the inguinal lymphatic region to the contralateral pelvic region has not been observed clinically or by lymphoscintigraphy. Although there is individual variation, on average the number of lymph nodes in the inguinal region is 10-20. The majority are located in the superficial region with only a minority (on average 3-5) in the deep inguinal region. The same amount of lymph nodes is found in the pelvic region.17

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