Introduction

The use of lymphatic mapping and sentinel node detection for cutaneous melanoma and breast cancer has been extensively investigated, and now minimally invasive sentinel node biopsy, which is associated with significantly less morbidity, has successfully replaced complete nodal dissection for nodal staging. This minimally invasive approach has been evaluated in several studies in patients with gynecologic malignancies, which have shown it to be capable of accurately identifying sentinel nodes. SPECT/CT provides both anatomical and functional information about the sentinel lymph node. We report the utility of hybrid SPECT/CT in localization of sentinel lymph node in a case of vulvar cancer.

Case Report

A 40 year old female presented with bleeding vulvar ulcer on the right side (T1 stage tumor). A biopsy from the edge of the ulcer revealed squamous cell carcinoma. The patient was planned for definitive surgery. A sentinel lymph node dissection was planned. Methylene blue dye was not used. Technetium-99m labeled unfiltered sulfur colloid was used and injection performed on the day of the surgery. Radiotracer in a dose of 100 microcurie each was injected at four sites around the tumor. Multiple static images were acquired till the visualisation of the sentinel lymph node. A hybrid SPECT/CT was performed immediately after visualisation of the sentinel lymph node. A focus of tracer uptake was noted in the planar image in the left inguinal region at 90 min after the injection. SPECT/CT localized the tracer uptake in a 1.2 cm sized left inguinal lymph node (Figure 1 and 2). The exact anatomical location of the lymph node and its relation with the adjacent structures were also defined by SPECT/CT. The left inguinal lymph node was successfully localized with an intra-operative probe and was subjected to histopathological examination. No metastases were noted in the lymph node on pathological examination. An unnecessary lymphadenectomy was avoided and the patient is on follow up without evidence of disease progression.

Discussion

Finding of positive sentinel nodes at surgery significantly influences staging and subsequent clinical management. In particular, a sentinel lymph node free from tumor metastasis would exclude tumor spread to the at-risk regional lymphatic basin. Although it is possible that a negative sentinel lymph node corresponds to metastatic involvement of a second-tier lymph node, this occurrence is very rare, especially when the primary tumor is in an early stage of growth. The sentinel node concept remains thus valid in most patients.

Studies have shown the efficacy of sentinel node mapping in cutaneous melanoma (1,2). Sentinel node mapping has been shown to be effective in gynecologic malignancies (3,4) including vulvar cancer (5,6). The accurate localization of sentinel nodes for tissue sampling has become increasingly important for clinical management. Preoperative SPECT/CT lymphoscintigraphy is ideal in this regard because it can map unpredicted lymphatic drainage pathways within the complex pelvic anatomy (7,8). SPECT/CT is able to achieve the precise anatomic localization of sentinel nodes on cross-sectional imaging, especially in relation to known anatomic structures such as the femoral or saphenous vein, information that is critical in planning the surgical approach. SPECT/CT also increases the sensitivity of sentinel node detection (9). A node close to the injection site can also be masked as the result of strong activity from the injection site (ie, the “shine through” effect). SPECT/CT avoids this problem and improves the detectability of the lesion (10). SPECT/CT has the potential to revive the usage of sentinel lymph node dissection.