Case Author(s): Jeffrey N. Yu, MD and Barry A. Siegel, MD , 5/2/2000 . Rating: #D2, #Q3

Diagnosis: Sentinel lymph node mapping: left shoulder malignant melanoma

Brief history:

21-year-old man who had prior resection of a 1.2-cm left shoulder malignant melanoma on 8/20/99.

Images:

Anterior dynamic flow images.

View main image(lm) in a separate image viewer

View second image(lm). Spot emission and transmission images.

Full history/Diagnosis is available below

Diagnosis: Sentinel lymph node mapping: left shoulder malignant melanoma

Full history:

21-year-old man who had a 1.2-cm malignant melanoma resected from his left shoulder 2 months before this study. The original lesion extended 1.21 mm into the dermis (Breslow thickness). This study is being performed to locate sentinel lymph node(s).

Radiopharmaceutical:

0.23 mCi millipore-filtered Tc-99m sulfur collid injected intradermally at six sites surrounding the scar on the left shoulder

Findings:

Serial dynamic scintigrams were obtained and demonstrated lymphatic drainage to the axilla. Two lymph nodes became apparent approximately simultaneously, one in the anterior axilla and another in the posterior axilla. The skin overlying these lymph nodes was marked. It should be noted that the depth of the posterior axillary lymph node is unknown, and it is possible that it is deep to the scapula. The patient tolerated the procedure well and without complaint.

Discussion:

Lymphoscintigraphy is indicated to determine the lymphatic drainage of a tumor, particularly malignant melanoma and breast carcinoma. The goals are to:(1) identify the sentinel lymph nodes; and (2) determine the sites of lymphatic drainage.

In cutaneous malignancies such as melanoma, drainage can be variable. For example, a site on the shoulder could drain to lymph nodes in the neck, the supraclavicular region, the axilla, or the mediastinum. Thus, it is important to define the nodes draining the area of interest. The first set of nodes that drain the area of interest are called the "sentinel nodes."

Performing this study within 1-2 weeks of an excisional biopsy may decrease the sensitivity for detecting the normal lymphatic drainage to the sentinel nodes. The presumed mechanism for this adverse effect is "clogging" of the lymphatic channels and lymph nodes by the debris cre- ated by the excisional biopsy. It is not clear, based on published data, whether this is an important practical issue.

The lymphatic draininage of a cutaneous lesion can be mapped by injecting millipore-filtered sulfur colloid intradermally around the lesion. Injecting directly into the lesion is not recommended as the lymphatic channels may be disrupted by the growth of the malignancy. The sulfur colloid will be collected and drained by the lymphatics and subsequently phagocytosed by macrophages within the sentinal lymph nodes. Typically, a 60-frame (30 seconds per frame) dynamic study is obtained for 30 minutes followed by static images obtained 2-3 hours post-injection. Foci of increased radiotracer accumulation do not necessarily represent lymph nodes involved by malignant disease as the tracer is not specific for malignant cells. Rather, the tracer identifies the first lymph nodes that filter the lymphatic drainage from an area of interest.

A transmission scan can be performed to assist in anatomically localizing the sentinel nodes. A brief (10 -econd) transmission image with a Co-5) flood source positioned behind the patient will outline the contour of the body. Alternatively, a small syringe of Tc-99m pertechnetate could be used as a marker to "trace" an outline of the body contour. Further localization is performed via surface marking and, depending on the surgeon, via a gamma probe during surgery. Once these nodes are located, they can be excised and examined for histologic or immunohistochemical evidence of metastatic disease.

Followup:

The patient had undergone resection of the melanoma in Korea two months before this study and had not had any adjuvant chemotherapy. Sentinel node dissection was performed with guidance from the lymphscintigraphy. Of the four nodes resected, two were positive for tumor and two were negative for malignancy.

Major teaching point(s):

1) Lymphoscintigraphy technique

2) Lymphoscintigraphy maps lympatic drainage, not tumor spread

3) A transmission image helps provide anatomic landmarks for localization

4) Lymphoscintigraphy can help localize nodes during surgery

ACR Codes and Keywords:

References and General Discussion of Lymphoscintigraphy (Anatomic field:Vascular and Lymphatic Systems, Category:Neoplasm, Neoplastic-like condition)

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Case number: lm003

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