Approach Considerations
The hypothesis of sentinel node dissection is that, if one or more sentinel lymph nodes are negative for malignancy, the remaining regional lymph nodes will also be negative. At least in theory, if the sentinel node shows no evidence of metastatic involvement, a complete node dissection can be avoided.
Sentinel Node Biopsy for Vulvar Cancer
Two techniques have been studied extensively in several case series, one with the injection of the primary tumor with isosulfan blue dye and the other with injection of radiotracer (99m Tc nanocolloid) involving lymphoscintigraphy with intraoperative gamma probe detection. Although the rate for sentinel node detection with blue dye can be reasonably accurate, the learning curve is steep, and the surgeon usually needs to perform many cases to achieve successful sentinel node identification. Most studies report an unacceptable failure rate (30%-40%) in sentinel node detection using blue dye alone. In contrast, studies of99m Tc nanocolloid, with or without isosulfan blue dye, have noted very high identification rates of sentinel nodes, [28] most 95%-100%. [1, 4, 28, 29]
Both techniques require several intradermal injections around the vulvar lesion, followed by massage of the area to help disperse the material. The radiotracer nanocolloid is injected one day to several hours preoperatively, whereas the isosulfan blue dye is injected intraoperatively. Clinical studies support using a combination of both agents for optimal results. [1, 4, 28, 29] Most panelists from the International Sentinel Node Society Meeting in 2008 perform preoperative planar lymphoscintigraphy, which helps to identify the number and general location (unilateral or bilateral) of the sentinel nodes. [12] Intraoperative gamma probe may assist in initial identification of the site and size of lymph nodes. [12, 30, 31]
A groin incision is made down to the level of Camper fascia. Careful dissection should allow for identification of blue afferent lymphatic channels, which lead to sentinel nodes, identified with blue staining and/or gamma probe detection (see images below).
Special attention should be paid to the medial bundle of nodes over the adductor longus muscle and medial to the femoral vessels. Intraoperative failure to identify the sentinel node(s) requires a complete inguinofemoral lymphadenectomy.
In patients with midline lesions, defined as less than 1 cm from the midline, an attempt should be made to identify sentinel nodes in each groin. If a sentinel lymph node is not found bilaterally, then a full inguinofemoral dissection is indicated on the side without the sentinel node. [12]
The optimal method for histopathological sentinel lymph node examination in vulvar cancer has not been established and is not standardized. Several case series advocate for ultrastaging of the sentinel node using smaller sections and/or immunohistochemistry, given that routine examination may not allow for identification of micrometastasis. [4, 13, 14, 28, 29]
The method of ultrastaging varies by series and institution. Many pathologists advocate starting with routine sectioning of the sentinel node and, if initially negative, proceeding with even smaller sections. Some also include the use of immunohistochemistry in their evaluation of sentinel nodes.
Puig-Tintore et al reported on a series of 26 patients without clinically suspicious adenopathy who underwent sentinel node biopsies using isosulfan dye and99m Tc nanocolloid. When the sentinel node was negative using conventional pathologic examination, none of the remaining lymph nodes in the groin revealed metastatic disease, confirming a 100% negative predictive value. In addition, no groin relapses were noted in patients with a negative sentinel node at 18.5 ± 9.4 months, providing long-term reliability for this method. However, ultrastaging in this group of patients did identify an additional 38% of sentinel nodes with micrometastatic disease. [4] This finding is similar to that of Van der Zee et al, who reported an increased detection rate of micrometastases in sentinel lymph nodes of 41.7% with ultrastaging. [13]
In contrast, in a de Hullu et al (2000) study of 59 patients who had 102 nodes removed, ultrastaging and immunohistochemistry increased the detection for metastatic disease by only 4%. [14] Two other studies found no increase in the detection of nodal metastases using ultrastaging versus serial sectioning and hematoxylin and eosin staining. [32]
Currently, the consensus is to complete the lymphadenectomy if micrometastases are found in the sentinel lymph nodes. [29] Investigators do not agree about the prognostic significance of micrometastases and the need for adjuvant therapy.
Sentinel Node Biopsy for Cervical Cancer
Most studies advocate the dual use of preoperative injection of radiolabeled Tc-99M microsulfur colloid and the intraoperative injection of isosulfan blue dye. [33] Cervical injection of radiolabeled colloid, either at 4 quadrants of the cervix or at 3 o’clock and 9 o’clock into the stroma of the cervix is performed either the day prior to the surgery or the morning of surgery. Intraoperative localization of the sentinel nodes is directed by a preoperative lymphoscintigraphy.
After induction of anesthesia, the isosulfan blue is injected in the operating room in a similar fashion, divided into 2 or 4 separate injections, as noted above.
Potential adverse effects of isosulfan blue may range from local allergic reactions (swelling and pruritus of the hands, feet, abdomen, or neck) to more severe reactions, including edema of the epiglottis, respiratory distress, shock, or transient drop in oxygen saturation. [34]
Once the abdomen is opened, the sentinel nodes are identified as being "hot" and/or "blue." Laparoscopic or open gamma probes are used to detect hot nodes, and, after excision, a postexcision bed count of each lymphatic basin should be recorded.
A 2014 study by Jewell et al suggests that near-infrared (NIR) fluorescence imaging in conjunction with intracervical indocyanine green (ICG) for detection of sentinel lymph nodes in cervical and uterine malignancies in minimally invasive surgery is favorable to use of blue dye alone and/or with other modalities. [35] In their cohort of 227 patients, the investigators reported sentinel lymph nodes were detected in 95%, with bilateral mapping in 79%, and an aortic sentinel lymph node was detected in 10% of the mapped cases. When mapping cases with ICG alone, the detection rate was 95%, whereas use of ICG with blue dye for mapping led to a 93% detection rate. [35]
A particularly challenging aspect of sentinel node biopsy in cervical cancer involves detecting parametrial sentinel nodes. The gamma probe detects radiocolloid in the cervical injection site, which interferes with accurate detection of parametrial lymph nodes. The blue dye commonly dissipates in the paracervical tissue and complicates visual isolation of a blue node. Although the most common site of the sentinel nodes is in the obturator nodal bed, other sentinel nodes may be found in the external iliac, common iliac, internal iliac, and paraaortic lymph nodes (see image below). [34]
Similar to the concept in vulvar carcinoma, ultrastaging and immunohistochemistry have resulted in increased detection of lymph node micrometastases, with varying frequency of micrometastases based on diverse ultrastaging techniques and terminology. [15, 19, 22, 36, 37]
In their case series of patients with cervical cancer, Euscher et al demonstrated a 25% increase in metastases detection rate attributed to ultrastaging of the sentinel nodes. [22] Diaz et al noted an additional 29% of patients with metastatic lymph nodes detected with ultrastaging only. [19]
Several series have shown a significantly reduced recurrence-free survival rate in patients with micrometastases and suggest that micrometastatic disease represents an independent prognostic factor in cervical cancer. [37] This observation may explain recurrence rates of up to 40% in patients with cervical cancer with histologically negative lymph nodes with deep stromal invasion or lymph/vascular space involvement. [15]
-
Using the gamma probe to detect a hot spot in the inguinal area.
-
Blue-stained afferent lymphatic leading to blue-stained inguinal lymph node.
-
Diagram of lymphatic drainage of a lateral lesion. Most lymphatics flow through the superficial inguinal nodes, deep inguinal nodes, and the node of Cloquet to the pelvic lymph node chains. Deep inguinal node findings are positive approximately 3% of the time when superficial inguinal node findings are negative. Lymphatic mapping studies indicate that 13% of cases demonstrate findings consistent with flow to the pelvis that does not involve the node of Cloquet. If the lesion is in the anterior labia minor, then contralateral flow is demonstrated in 67% of cases.
-
A specimen from a traditional single-incision radical hysterectomy. Most radical vulvectomies are now performed through 3 incisions, with the groin nodes removed separately from the vulvectomy specimen. (Photograph courtesy of James B. Hall, MD)
-
Closure of a large single-incision radical vulvectomy. The complete wound breakdown rate from this procedure is often greater than 50%. (Photograph courtesy of James B. Hall, MD)
-
The parietal lymph glands of the pelvis.
