Imaging in Oncology
Imaging in Oncology (Answer)
Answer:
1. There can be more than one sentinel lymph node.
Discussion
Lymphoscintigraphy is the injection of radioactive particles around a tumor in an
effort to identify the lymph nodes that have afferent drainage from that tumor. A
selective lymph node sampling approach has been advocated based on lymphoscintigraphic
methods for identifying the sentinel lymph node (SLN), which is the first lymph node
draining the lesion. In both melanoma and more recently carcinoma of the breast,
techniques based on SLN identification have been shown to accurately predict the
pathologic status of the draining lymph node basin.1
At our institute, the technique of breast lymphoscintigraphy consists of a dose of 500
µCi of technetium-99m in 2 to 10 cc of diluent injected in six equal aliquots at the
periphery of the palpable tumor or seroma cavity. Injection into the tumor or seroma
cavity is avoided as this diminishes lymphatic flow. For nonpalpable lesions, the
radiopharmaceutical is administered in six equal aliquots around the localization needle
while the breast is in compression. The patient is then positioned supine beneath the
gamma camera. A large field-of-view scintillation camera with a high-resolution collimator
is used. The persistence scope is used to identify accumulations of the
radiopharmaceutical corresponding to lymph nodes. Internal mammary and supraclavicular
lymph nodes can be tattooed in the anterior projection, while the axillary lymph nodes are
tattooed with the patient in the lateral position with the arm above the head. Images are
acquired over five minutes per view to assure high count density. Images are obtained in
the anterior, lateral, and oblique positions. Imaging is performed immediately
postinjection. If there is no evidence of lymphatic flow, imaging following a two- to
four-hour delay can be helpful.
Since most breast carcinomas arise within the upper outer quadrant of the breast,
conventional wisdom holds that nodal drainage will be to the axilla, and only the most
medial tumors will drain to the internal mammary chain. Uren and colleagues2 studied
32 patients with antimony sulfur colloid lymphoscintigraphy and found that there was
ipsilateral axillary node drainage in 85% of cases. However, the multiplicity and
variability of drainage patterns were unexpected. Twenty-eight percent of patients with
outer quadrant tumors showed unexpected drainage to internal mammary nodes, while 33% of
patients with inner quadrant tumors showed axillary drainage. Thus, one third of patients
with lateralized tumors had drainage that crossed the midline of the breast. Of patients
with upper quadrant tumors, 20% showed direct drainage to supraclavicular or
infraclavicular nodes. In one patient, an intransit lymph node — a lymph node between
the lesion and the regional lymph node basin — was in fact the SLN and contained
metastatic disease. Standard axillary dissection would not have identified this node and,
by implication, the patient's need for systemic adjuvant therapy. The case presented shows
a lateral tumor that crosses the midline and has multiple drainage sites to both the
ipsilateral axillary and internal mammary chains.
Historically, the axillary lymph node drainage has been defined anatomically as levels
I, II, and III. Level III indicates nodes medial to the pectoralis minor muscle, level II
indicates those deep to the muscle, and level I indicates those lateral to the muscle. In
our series, 12% of SLNs were in level II only.3 The lymphoscintigram provides
the surgeon with this information to aid in surgical planning. An important advantage of
our technique is that it tracks the physiologic pathway(s) for the given lesion, allowing
a focused dissection based on the particular in vivo physiology rather than on arbitrary
anatomic designations.
Preoperative breast lymphoscintigraphy offers the opportunity for identification of the
unique pattern of nodal drainage for each malignant lesion. Directing the surgeon to the
site of the SLN minimizes the operative time, the extent of dissection, and the likelihood
of late morbidity. Identification of in-transit lymph nodes detects a subset of patients
inadequately examined by standard axillary dissection techniques. Identification of
internal mammary SLNs allows for rational radiotherapeutic planning in patients who might
not otherwise be recognized as high risk.
References
- Alazraki N. Lymphoscintigraphy and the intraoperative gamma probe. J Nucl Med.
1995;36:1780-1783.
- RF, Howman-Giles RB, Thompson JF, et al. Mammary lymphoscintigraphy in breast cancer. J
Nucl Med. 1995;36:1775-1780.
- Albertini JJ, Lyman GH, Cox C, et al. Lymphatic mapping and sentinel node biopsy in the
patient with breast cancer. JAMA. 1996;276:1818-1822.
Back to Cancer Control
Journal Volume 4 Number 6