Koos Boeve

91 Lymphatic drainage patterns of oral maxillary tumors Sentinel lymph node procedure The SLNB procedure was performed as described earlier [23]. Briefly, 1 day before operation 99m Tc-nanocolloid was injected peritumorally at 4 locations; median 100 MBq (range 60- 100 MBq). Slow infiltration of the tracer is required to inject successfully in the oral maxilla without leakage. Injection was immediately followed by dynamic lymphoscintigraphy for 20 minutes in anterior or oblique views (20 x 60 s, 128 x 128 matrix) and static images (300 s, 256 x 256 matrix) in 2 directions; anterior and lateral. The static images were repeated after 2 to 4 hours, followed by a Single Photon Emission Computed Tomography (SPECT)-CT scan of the head and neck using a 2-headed gamma camera equipped with parallel-hole ultra-high resolution collimators and a 2-slice CT scanner (32 views of 20 s, 128 x 128 matrix; mAs 30, kV 110, 3.0 mm slice; Siemens, Knoxville, TN). After these images, the position of the sentinel lymph node was marked on the overlying skin by using a 57 Cobalt point-source- marker and a γ-probe. The first focus on lymphoscintigraphy, in any direction of the tumor, was considered as the sentinel lymph node. All the lymph nodes with their own lymphatic track directly from the tumor were marked as sentinel lymph node. Neither number nor neck level were restricted for the sentinel lymph nodes. The lymphoscintigraphy images used in this study were all revised by a senior nuclear medicine physician (A.H.B.). Surgical procedure Patients were operated within 24 hours after the lymphoscintigraphy with resection of the tumor and staging of the neck by SLNB. In 5 patients, this was combined with a neck dissection. The SLNB side depended on the location and size of the tumor and prior neck treatment. In case of a small tumor, a tumor close to the midline, or a tumor crossing the midline, respectively, an ipsilateral, contralateral, or bilateral SLNB was indicated (Table 2). All lymph nodes with a high signal on the γ-probe at the marked position on the skin were harvested and marked as sentinel lymph nodes. Because of the conglomeration of lymph nodes, it is not always possible to separate 1 lymph node with a high signal during an operation. In that case, more harvested lymph nodes were marked as SLNs at one location. In several patients, a few additional non-radioactive lymph nodes close to the sentinel lymph node were also harvested to ensure sentinel lymph collection. These additional lymph nodes were separated ex vivo from the sentinel lymph nodes by using the γ-probe. Blue dye was not used intra-operatively in our cohort. Histopathological examination The histopathological examination of the sentinel lymph node is also described earlier [23]. Briefly, step-serial-sectioning of the entire sentinel lymph node was performed in our center with an interval of 500 µm. All levels were stained with hematoxyline-eosine and for immunohistochemistry with pan-cytokeratin antibody (AE 1/3). The additionally harvested