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Pathological evaluation of melanocytic lesions


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In this lecture, the following basic steps by which I routinely scan specimens in our hospital will be presented with examples.
1. Evaluate the specimen preparation.
1) Is the incision for the specimen made perpendicular to the skin surface?
2) Is the slice of tissue from volar skin made perpendicular to the furrows of skin?
2. Estimate the specimen size and location.
1) Estimate the size of the lesion from the magnification of the objective lens.
2) Estimate the specimen location.
3. Precaution before evaluation
1) Observe the specimens without clinical information as much as possible.
2) Obtain as much information as possible at low magnification.
4. The steps for observation
1) At low magnification: Check the symmetric properties and circumscription of the lesion based on the following points.
a. Distance from the densest area of the lesion to both ends.
b. Variation of the thickness of epidermis from the center to both ends.
c. Distribution of melanin in the coronoid layer, epidermis, and dermis.
d. Distribution of nests and distance between each nest.
e. Density of solitary distributed melanocytes.
f. Existence of inflammatory infiltration in the dermis and its distribution.
g. Continuity of the spread of nests and tumor cells in both ends.
h. Is the bottom of the lesion smooth or not?
2) At high magnification: Check the details of tumor cells.
a. Tumor cells in the epidermis: Existence of necrosis, atypia (large nucleolus), or mitosis.
b. Other findings in the epidermis: Distribution of melanin in the cornified layer, the existence of tumor cells in the upper epidermis, the polymorphism of tumor cells, the relationship between tumor cells and keratinocytes.
c. In the dermis: An overlapping, crowded, or sheet-like gathering of tumor cells, maturation of tumor cells, mitotic figures, or melanin of tumor cells at the bottom of the lesion.
d. In the adnexal area: The existence of tumor cells in adnexal walls.
5. After provisionally giving a pathological diagnosis, check discrepancies between the pathological diagnosis and clinical findings. Return to the pathological evaluation if necessary.

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Pathological evaluation of melanocytic lesions

  1. 1. Pathological evaluation of melanocytic lesions Hisashi Uhara, MD. Associate professor Department of Dermatology, Shinshu University School of Medicine Asahi 3-1-1, Matsumoto, Japan
  2. 2. Contents 1.Preparation before observation 2.Clues suggesting melanoma 3.Clinical findings to avoid over diagnosis
  3. 3. 1. Preparation
  4. 4. Preparation 1 Evaluate specimen
  5. 5. Evaluate the specimen (1) Go! If the specimen is made perpendicular to the skin surface. (This is a good specimen because the width of epidermis is entirely same and it is arrayed parallel).
  6. 6. Stop! In These bad specimens, nests or melanocytes are frequently seen in the upper part of the epidermis
  7. 7. Go! Stop! Evaluate the specimen (2) The slice should be made perpendicular to the furrows of skin, especially important in lesions of palm or sole. In the section like this, solitary and irregular proliferation are frequently seen even if it was originally a common nevus with regular nests
  8. 8. Preparation 2 Free from clinical information This way has 2 benefits. One is that we can avoid a bias affected by a clinical information. The other is that it may become good training for us to get a pathological skill.
  9. 9. Preparation 3 Start at low magnification By Dr. Ackerman
  10. 10. 2. Clues suggesting melanoma
  11. 11. 13 findings to be checked
  12. 12. 1/13 Size?
  13. 13. 5mm 5mm Caution
  14. 14. 2/13 Solitary > Nests? VS X
  15. 15. Solitary proliferation of melanocytes
  16. 16. Space In low magnification, multiple small and irregular spaces may be clue to showing solitary proliferation.
  17. 17. 3/13 Symmetric? (1) Distance from the center (2) Condition of epidermis (3) Distribution of nests (4) Distribution of melanin (5) Distribution of inflammation (6) Heterogeneity of tumor cells
  18. 18. 3/13Symmetric? (1) Distance from the center
  19. 19. 3/13Symmetric? (2) Thickness of epidermis from the center to both ends
  20. 20. 3/13Symmetric? (3) Distribution of nests & melanocytes
  21. 21. Equidistance? VS
  22. 22. (3) Distribution of spaces (melanocytes) You can see randomly distributed spaces.
  23. 23. 3/13Symmetric? (4) Distribution of melanin in the cornified layer, epidermis, and dermis
  24. 24. In this specimen resected from acral region, you can see nests in the basal layer not only under the surface furrow but also under the surface ridge. Ridge dominant proliferation of melanocytes or melanin deposition show clinically parallel ridge pattern, suggesting melanoma. But, in melanin stained section, melanin columns are only seen under the furrows but not ridges. So, this is benign nevus. Saida T, Koga H, Goto Y, Uhara H. Characteristic distribution of melanin columns in the cornified layer of acquired acral nevus: an important clue for histopathologic differentiation from early acral melanoma. Am J Dermatopathol 2011 Jul;33(5):468-73.
  25. 25. Symmetric? (4) Distribution of melanin (melanophage) in epidermis and dermis VS X
  26. 26. 3/13 Symmetric? (5) Inflammatory infiltration
  27. 27. (5) Inflammatory cells VS x
  28. 28. 3/13 Symmetric? (6) Heterogeneity of tumor cells
  29. 29. Round Spindle x
  30. 30. 4/13 Circumscription? Nests & melanocytes
  31. 31. 5/13 Melanocytes in upper epidermis
  32. 32. “ascent” or “casting off” is bad sign.
  33. 33. 6/13 Size of Nests & melanocytes
  34. 34. Size of nests & melanocytes VS x
  35. 35. 7/13 Confluent? In dermis The distribution of nevus cells is confluent or cluster?
  36. 36. Sheet
  37. 37. Relationship Nests, melanocytes & collagen bundles VS Spitz Melanoma
  38. 38. 8/13 Shape of bottom?
  39. 39. Shape of bottom FLA VS Flat Wedge shaped X
  40. 40. 9/13 Melanocytes in adnexal walls Melanocytes in adnexal walls are also seen in benign lesions such as congenital nevus. But, if you find solitary proliferation of melanocytes in lower potion of adnexa, it is finding to be cared.
  41. 41. High magnification 10/13 Atypia 11/13 Mitosis 12/13 Necrosis 13/13 Maturation
  42. 42. 10 Atypia? Big and red nucleorus
  43. 43. 10 atypia 11 necrosis 12 mitosis Presence & Distribution in the bottom of the lesion
  44. 44. 13 Maturation
  45. 45. Easilear obtainable findings 1 Size (>5mm) 2 Solitary proliferation 3 Symmetry (epidermis, melanin, lymphocytes) 4 Circumscription 5 Melanocytes in upper epidermis 6 Size of nests 7 Confluent 8 Shape of bottom 9 Melanocytes in adnexal walls 10 Atypia 11 Mitosis 12 Necrosis 13 Maturation
  46. 46. 3. Clinical findings to avoid over diagnosis Last step
  47. 47. Check clinical information Check discrepancies between the pathological diagnosis and clinical findings. If necessary, return to the pathological evaluation.
  48. 48. Clinical signs to pay attention when your diagnosis is malignant > benign
  49. 49. Age Children The specimen removed from infants and children frequently shows atypical findings, such as remarkable atypia, necrosis, and mitosis.
  50. 50. Location Mucosa (eyelid, genital) Nail Palm & Sole
  51. 51. History of resection Recurrent nevus after initial resection shows irregular findings like melanoma.
  52. 52. Halo nevus
  53. 53. Spitz nevus
  54. 54. If your diagnosis….melanoma? Check !! Age Location History Halo Spitz
  55. 55. 1. Check condition of specimen 2. Without clinical information 3. At low magnification
  56. 56. If first impression……. Benign? Check 13 pathological findings + dermoscopy If first impression….. Malignant? Check 5 clinical findings
  57. 57. Thank you