Posterior views of the lower extremities centered just proximal to the left heel intradermal injection site at 1-2 minutes post injection.
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View second image(lm). Emission images on the left and transmission images on the right. Posterior feet (top), posterior knees (middle), and anterior inguinal region (bottom).
Full history/Diagnosis is available below
The two popliteal and the sentinel inguinal lymph nodes were marked on the skin for surgery.
A number of radionuclides have been employed in lymphoscintigraphy. The earliest of these radionuclides was gold (198Au) colloid, however, its dosimetry was unacceptable. Currently used lymphoscintigraphic agents are the Tc-99m-labeled radiocolloids, including Tc-99m sulfur colloid and Tc-99m antimony sulfide colloid, as well as Tc-99m human serum albumin (HSA). Following the interstitial injection, the radiocolloids enter the lymphatic capillaries and travel to the regional lymph nodes where they accumulate in the macrophages. The degree of nodal uptake of radiocolloid is highly dependent upon the size of the particle. The optimal radiocolloid size for lymphoscintigraphy has been reported to be 10-50 nm. Presently, Tc-99m antimony sulfide colloid available is not available in the United States, and filtered Tc-99m sulfur colloid is typically used. The large particle size of conventional Tc-99m sulfur colloid is not ideal as most of the activity will remain localized at the injection site. However, smaller particle size can be achieved with millipore filtration prior to injection. Tc-99m HSA can be used to define lymphatic channels, but has substantially less retention in lymph nodes.
Lymphoscintigraphy plays an important role in the work-up of patients with melanoma, especially in those patients with truncal melanoma as the typical lymphatic drainage pathways are often unpredictable in truncal melanoma. The popularity of lymphoscintigraphy in patients with melanoma also stems from the concept of the sentinel node, which is defined as that lymph node in a given lymphatic chain that is the first to receive lymphatic flow from a primary tumor site. It is presumed that the progression of nodal metastases in a given chain occurs in an orderly fashion. That is, if the sentinel node is negative for tumor, the remaining lymph nodes in that chain should also be negative. This has been confirmed in multiple studies where both sentinal node dissections and subsquent full nodal dissections were performed. The sentinel node concept has revolutionized the management of melanoma patients, with fewer elective lymph node dissections now being performed.
References: 1. Ziessman HA and Kaplan WD. Hepatic arterial perfusion scintigraphy and radionuclide lymphoscintigraphy. In: Sandler MP et al., ed. Diagnostic Nuclear Medicine, 3rd edition. 1996;1313-1321. 2. Gulec SA, Moffat FL, and Carroll RG. The expanding clinical role for intraoperative gamma probes. In: Freeman LM, ed. Nuclear Medicine Annual 1997. 1997;209-237.
The identification of lymph nodes draining the primary tumor does not imply that these lymph nodes are malignant.
References and General Discussion of Lymphoscintigraphy (Anatomic field:Vascular and Lymphatic Systems, Category:Neoplasm, Neoplastic-like condition)
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