First published online May 25, 2006
British Journal of Radiology (2007) 80, 132-139
© 2007 British Institute of Radiology
doi: 10.1259/bjr/20286459
Pearls and pitfalls of radionuclide imaging of the lymphatic system. Part 1: sentinel node lymphoscintigraphy in malignant melanoma
A F Scarsbrook, BMBS, BMedSci, FRCR
A Ganeshan, MRCP
and
K M Bradley, MRCP, FRCR
Department of Radiology, John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DU, UK
Correspondence: Dr Kevin Bradley, Consultant Radiologist & Nuclear Medicine Physician, Department of Radiology, John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DU, UK
 |
Abstract
|
|---|
Radionuclide imaging of the lymphatic system has a major role in the management of two main patient groups. First, pre-operative lymphoscintigraphy is a highly accurate method of sentinel node localization and can help guide minimally invasive surgery in a variety of tumour groups. Second, lymphoscintigraphy can play a pivotal role in assessing the cause of extremity swelling. This is the first of two pictorial essays on radionuclide imaging of the lymphatic system and will focus on sentinel node imaging in malignant melanoma. Regional nodal sampling is routinely performed in an increasing number of tumour groups and is well established in malignant melanoma and breast carcinoma. Careful attention to technical performance and image interpretation is essential to maximize the clinical utility of the test. This article provides a pictorial review of the interpretative pearls and pitfalls of sentinel node lymphoscintigraphy in malignant melanoma patients.
|
Introduction
|
|---|
Regional lymph node sampling is routine practice in the staging of many common malignancies. Lymphoscintigraphy is a highly sensitive method for mapping lymphatic drainage from tumours and is widely used in malignant melanoma and breast carcinoma patients [1–3]. The technique shows promise in penile, vulval, prostate, bladder, colorectal, gastro-oesophageal, and head and neck tumours, but is not widely used in these tumours at present [4–6].
Cutaneous melanomas originate from cells located between the dermis and epidermis and drain to the lymphatic network in the reticular dermis. Therefore radiopharmaceuticals are best administered via intradermal injection in melanoma patients. Radiolabelled micro-particles instilled around superficial tumours drain through lymph vessels to regional nodes. This allows the regional node(s) directly receiving lymph from the tumour, the sentinel node(s), to be accurately identified and facilitates minimally invasive nodal resection. If no tumour is present within the sentinel node, a radical lymph node dissection can be safely avoided and surgical morbidity minimized. The success rate of sentinel node localization in malignant melanoma approaches 100% in experienced hands, especially if combined with blue dye and an intraoperative gamma probe.
The ideal lymphoscintigraphic agent is safe, rapidly clears from the interstitium into the lymphatic system, produces high quality images and delivers a low radiation dose to the patient. In addition, retention of the radiopharmaceutical in the region of interest is vital for successful localization. Large radiopharmaceutical particles (>500 nm diameter) tend to remain at the site of injection and poorly demonstrate the lymphatic system. Smaller particles (<100 nm) are optimal for sentinel node lymphoscintigraphy (SNL). A number of different radiopharmaceuticals possess these properties and are in routine use. In America, filtered 99Tcm sulphur colloid (particle size 
40 nm) is the most commonly used agent [1]. Throughout Europe, including in our institution, 99Tcm-albumin nanocolloid (particle size <5–80 nm) is used. There is no discernable difference in the sensitivity of SNL between different radiocolloids in malignant melanoma patients [7].
We present a pictorial review of SNL in melanoma with an emphasis on key interpretative pearls and pitfalls. Whilst the principles of SNL are the same irrespective of the tumour type, malignant melanoma demonstrates the greatest variation in lymphatic drainage, and therefore the biggest challenge in technique and accurate localization.
|
Sentinel node imaging technique
|
|---|
Four intradermal injections of 5–10 MBq of radiotracer (diluted in 0.1 ml of saline) are instilled closely around the tumour site or mid-point of the primary excision scar. Immediate dynamic imaging with the injection site in the field of view is performed. Images are acquired every 30–60 s to identify lymphatic drainage and continue until the sentinel node has been demonstrated or for 30 min, whichever is sooner. A large field-of-view detector with a parallel hole, high resolution collimator should ideally be used. Once the sentinel node(s) has been identified (usually within the first 30 min), additional static views in various planes are obtained to confirm the position of the node and identify any additional sentinel nodes at unsuspected drainage sites prior to marking. If no nodal uptake has been demonstrated after 30 min, the dynamic acquisition is stopped and static views in two planes are obtained to exclude a sentinel node(s) obscured by the injection site or additional superimposed nodes. If this is not the case, further delayed images are obtained until the sentinel node(s) are demonstrated. In most cases this is within 2 h, but may be as long as 6 h in our experience.
A 57Cobalt flood source can be used to provide an outline of the patient's body, which is useful for anatomical localization and to aid the surgeon (Figure 1
). Once the sentinel node(s) have been identified, the overlying skin is marked with the patient in the same position as for surgical excision, with the aid of a 57Cobalt pen. Within 24 h of the investigation, patients are taken to theatre. An intraoperative gamma probe and blue dye injection guide minimally invasive excision of the sentinel node. In our experience, provided sufficiently delayed images are obtained the failure rate of SNL in melanoma is less than 1%.
View larger version (132K):
[in this window]
[in a new window]
|
Figure 1. Lymphatic vessel drainage. Image from a 31-year-old male with a left anterior abdominal wall melanoma showing two prominent lymphatic vessels draining to a solitary left axillary sentinel node. Also note the hepatic uptake and a second echelon node within the axilla (arrow). The outline of the patient's body is obtained by using a 57Cobalt flood source to provide a transmission image.
|
|
|
Sentinel node imaging pearls
|
|---|
We have developed a number of interpretative pearls which can be used to maximize the diagnostic utility of SNL and minimize false positives or negatives, these are illustrated below. The potential pitfalls of the technique are also demonstrated.
Early dynamic imaging allows visualization of lymphatic vessels (Figure 1
) and maps the lymphatic drainage to regional nodes, an essential prerequisite of the technique. The pattern of lymphatic drainage is highly variable between individuals [3, 8]. In many cases there is drainage to a solitary regional sentinel node (Figure 2). However, for melanomas located in the midline of the head, neck and trunk, particular consideration should be given to unexpected lymphatic drainage and all potential regional nodal sites should be imaged. Drainage to an additional sentinel node in a different anatomical site may be obvious (Figure 3a) or subtle (Figure 3b).
View larger version (85K):
[in this window]
[in a new window]
|
Figure 2. Solitary sentinel node. Early(5 min) (a) frontal and (b) lateral images from a sentinel node scintigram in a 39-year-old female with a cutaneous malignant melanoma on the left shoulder demonstrating lymphatic drainage to a solitary left axillary sentinel node (arrows).
|
|
View larger version (59K):
[in this window]
[in a new window]
|
Figure 3. Multiple sentinel nodes.(a) Frontal image from a 43-year-old female with a central anterior abdominal wall melanoma demonstrating lymphatic drainage to bilateral axillary sentinel nodes, a secondary left axillary node is also noted (thin arrow). (b) Frontal image from a 35-year-old male with a melanoma on the left side of the trunk showing bilateral axillary sentinel nodes, the right sided node is more conspicuous on this image due to careful windowing, but could easily be overlooked. A lead shield has been used to avoid obscuration of a regional node by scatter from the injection site (thick arrow). The dome of the liver is seen in the lower portion of the image.
|
|
Drainage to interval nodes lying along the course of a lymphatic vessel between the primary tumour site and the regional nodal group is not uncommon, for example epitrochlear and axillary sentinel nodes in upper limb tumours (Figure 4a), or a chest wall sub-station node in tumours on the trunk (Figure 4b,c). Whilst early dynamic views are essential, delayed imaging is also important in order to detect delayed lymphatic drainage to other nodal groups (Figure 5). Delayed imaging is also useful for detection of sentinel nodes close to the tumour site, which may be obscured by scatter from the injected tracer on the early images (Figure 6).
View larger version (81K):
[in this window]
[in a new window]
|
Figure 4. Drainage to interval nodes.(a) Frontal image from a 56-year-old male with a melanoma on the right wrist demonstrating tracer uptake in a right epitrochlear node (arrow) and multiple right axillary nodes. The liver is seen in the lower portion of the image. Both the epitrochlear and sentinel axillary node were marked. (b) Early (5 min) and (c) delayed (30 min) prone images from a 27-year-old female with a right posterior chest wall melanoma show an unusual sentinel node on the posterior chest wall (b) (thin arrow) and subsequent uptake of tracer within a right axillary sentinel node (c). A lead shield was used to cover the injection site (thick arrows in (b) and (c)).
|
|
View larger version (87K):
[in this window]
[in a new window]
|
Figure 5. Importance of delayed imaging.(a) Early and (b) late frontal images from a 47-year-old male with a left anterior chest wall melanoma showing bilateral axillary sentinel nodes; the right is much more conspicuous on (b) the delayed (1 h) image and could easily have been missed. Lead shields have been placed over the injection site in the images (arrows).
|
|
View larger version (89K):
[in this window]
[in a new window]
|
Figure 6. Importance of additional imaging planes– obscuration by injection site. Frontal and lateral images from a 39-year-old male with a melanoma in the left cervical region. (a) The sentinel node is completely obscured by the injection site on the frontal image, but is clearly identified on (b) the lateral view (arrow). A lead shield has been placed over the injection site in (a) (arrow).
|
|
As in many other imaging techniques, careful patient positioning and imaging in more than one projection are essential to detect additional nodes, which may otherwise be missed on a single picture (Figure 7).
View larger version (75K):
[in this window]
[in a new window]
|
Figure 7. Importance of additional imaging planes– overlapping nodes. Frontal and lateral images from a 53-year-old female with a melanoma on the left posterior chest wall. (a) A solitary left axillary sentinel node (arrow) and two second echelon nodes are demonstrated on the frontal view. (b) The lateral image reveals that there are actually two sentinel nodes which are superimposed on the frontal view.
|
|
|
Sentinel node imaging pitfalls
|
|---|
Careful injection technique is essential to avoid contamination of the skin with the radiopharmaceutical, which will degrade images. Whilst this may be obvious (Figure 8a) and easily washed or cleaned before re-imaging, contamination can occasionally be very focal and mimic a sentinel node (Figure 8b,c) potentially leading to false positive localization. While marking the location of the sentinel node it is important to accurately mark the site and avoid inadvertent labelling of secondary nodes (which do not directly receive lymph) (Figure 9). Likewise, pooling of radiotracer within lymphatic channels can occasionally mimic a sentinel node and lead to false localization (Figure 10). This pitfall can usually be avoided by obtaining at least two views and, if there is a suspicion of pooling, further delayed images after 30 min usually clarify.
View larger version (110K):
[in this window]
[in a new window]
|
Figure 8. Skin contamination with radiotracer.(a) Frontal image showing bilateral axillary sentinel nodes in a 32-year-old male with an upper anterior chest wall melanoma, the image is degraded by multiple focal areas of increased tracer uptake over the right side of the scalp due to contamination. A lead shield has been placed over the injection site (arrow). (b) Frontal image from a 41-year-old female with a left chest wall melanoma showing a left axillary sentinel node and an area of abnormal uptake in the midline at the root of the neck which could represent a further node (arrow). (c) Following skin washing a repeat frontal image confirms that this area of abnormal update was due to skin contamination and not a node.
|
|
View larger version (122K):
[in this window]
[in a new window]
|
Figure 9. Multiple nodes– secondary nodes versus multiple sentinel nodes. (a) Frontal image from a 26-year-old female with a melanoma on the right calf (injection site not shown) demonstrating nodal uptake in three right inguinal nodes. The right thigh lymphatic vessel drains directly into the lowest node (arrow) which is the sentinel node. Lymph subsequently drains to the two further nodes and these are therefore secondary nodes and need not be marked. (b) Frontal image from a 46-year-old male with a left calf melanoma (injection site not demonstrated) showing two separate lymphatic vessels (arrows) draining into two left inguinal nodes, which are therefore both sentinel nodes and should both be marked for sampling.
|
|
View larger version (56K):
[in this window]
[in a new window]
|
Figure 10. Lymphatic pooling mimicking nodes. Early(5 min) and delayed (30 min) images from a 39-year-old male with a right sided chest wall melanoma. (a) Early frontal image showing apparent drainage to two right axillary sentinel nodes. (b) Delayed frontal image showing that one of the apparent nodes has disappeared; the appearance on the early image was due to lymphatic pooling. If the delayed images had not been performed, this may have been marked erroneously as an additional sentinel node.
|
|
|
Conclusion
|
|---|
Radionuclide imaging of the lymphatic system has a crucial role in sentinel node localization for an increasing number of tumour types. Careful attention to technical performance and image interpretation is essential to maximise the clinical value of the test. We have described a number of interpretative pearls and pitfalls to maximize the utility of the technique.
Received for publication November 7, 2005.
Revision received December 13, 2005.
Accepted for publication January 3, 2006.
|
References
|
|---|
- Yudd AP, Kempf JS, Goydos JS, Stahl TJ, Feinstein RS. Use of sentinel node lymphoscintigraphy in malignant melanoma. RadioGraphics 1999;19:343–53.[Abstract/Free Full Text]
- Uren RF, Howman-Giles R, Thompson JF. Patterns of lymphatic drainage from the skin in patients with melanoma. J Nucl Med 2003;44:570–82.[Abstract/Free Full Text]
- Krynyckyi BR, Kim C, Goyenechea MR, Chan PT, Zhang Z, et al. Clinical breast lymphoscintigraphy: optimal techniques for performing studies, image atlas, and analysis of images. Radiographics 2004;24:121–45.[Abstract/Free Full Text]
- Ege GN. Augmented iliopelvic lymphoscintigraphy: applications in the management of genitourinary malignancy. J Urol 1982;127:265–9.[Medline]
- Zuckier LS, Finkelstein M, Kreutzer ER, et al. Technetium-99m antimony sulphide colloid lymphoscintigraphy of the prostate by direct transrectal injection. Nucl Med Commun 1990;11:589–96.[Medline]
- Merrie AE, Van Rij AM, Phillips LV, et al. Diagnostic use of the sentinel node in colon cancer. Dis Colon Rectum 2001;44:410–7.[CrossRef][Medline]
- Wong JH, Terada K, Ko P, Coel MN. Lack of effect of particle size on the identification of the sentinel node in cutaneous malignancies. Ann Surg Oncol 1998;5:77–80.[CrossRef][Medline]
- Intenzo CM, Kim SM, Patel JI, et al. Lymphoscintigraphy in cutaneous melanoma: a total body atlas of sentinel node mapping. RadioGraphics 2002;22:491–502.[Abstract/Free Full Text]
This article has been cited by other articles:
|
|
|
|
 
C. M. Intenzo, C. A. Truluck, M. C. Kushen, S. M. Kim, A. Berger, and J. C. Kairys
Lymphoscintigraphy in Cutaneous Melanoma: An Updated Total Body Atlas of Sentinel Node Mapping1
RadioGraphics,
July 1, 2009;
29(4):
1125 - 1135.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. V. Mar, R. L. Dickinson, W. D. Erwin, and R. E. Wendt III
Optimal 57Co Flood Source Activity and Acquisition Time for Lymphoscintigraphy Localization Images
J. Nucl. Med. Technol.,
June 1, 2008;
36(2):
82 - 87.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
Abstract
Introduction
