What is PET CT?
Positron emission tomography-computed tomography is a nuclear medicine technique which combines a positron emission tomography (PET) scanner and a tomography (CT) scanner,
to acquire images that demonstrate the metabolism of a tissue.
The most used radiopharmaceutical is fludeoxyglucose F-18,
allowing to assess the tissue uptake of glucose.
What is cutaneous melanoma?
Cutaneous malignant melanoma is the result of uncontrolled proliferation and/or malignant transformation of the melanocytes located in the basal epidermal layer of human skin(1).
Other locations where melanocytes can be found: eyes,
ears,
gastrointestinal tract,
leptomeninges,
oral and genital mucosa(2).
Cutaneous malignant melanoma is lethal cancer whose incidence has been increasing exponentially in the last decades.
Melanoma Pathology
Melanocytes are cells that produce melanin,
at skin they provide melanin for the epidermal keratinocytes.
The secretion of melanin results in ethnic variability of skin color.
Those melanocytes that undergo malignant change show varied architectural patterns of growth.
This forms the basis of the histological sub-typing,
with the four most important/common sub-types.
Classification of Cutaneous Melanoma(3)
Sub-type |
Some characteristics |
Superficial spreading melanoma
|
It is the most frequent type,
involving lower extremities and back. |
Nodular melanoma |
It has a vertical growth pattern.
Appears mainly in trunk and limbs |
Acral lentiginous melanoma
|
It involves skin devoid of hair such as hands and feet |
Lentigo maligna melanoma
|
It's common in the face and neck of older patients. |
Multiple additional uncommon subtypes are also described based on a histopathology growth pattern,
there we have desmoplastic melanoma,
nevoid melanoma,
amelanotic melanoma,
and animal type melanoma.
Important factors to be considered at staging:
The initial diagnosis is clinical.
However,
it's necessary a histopathological confirmation and a microstaging with Breslow classification,
where melanomas more than 1 mm of depth should be evaluated in search of a sentinel lymph node(4).
Breslow |
Depth |
I |
<1mm |
II |
1mm - 2 mm |
III |
>2mm - 4mm |
IV |
>4 mm |
Those melanomas with a positive sentinel lymph node are candidates to a positron emission tomography (PET-CT) with 18 fluor deoxyglucose (18F-FDG)(5).
Defined as the absence of intact epidermis on the surface of primary melanoma.
The mechanisms of cutaneous melanoma dispersion are by lymphatic spread to loco-regional lymph nodes,
hematogenous dissemination,
and direct dissemination(6).
The term "loco-regional metastases" includes local recurrences,
in transit and satellite metastases,
and regional lymph node metastases.
Fig 1.
A sentinel lymph node is any lymph node which receives lymph drainage directly from a tumor site.
To identify one,
it's necessary to perform a lymphoscintigraphy to visualize the lymphatic collecting vessel on dynamic imaging as the direct drainage into the sentinel node(7).
Patterns of lymphatic drainage from the skin are variable from the same area of the skin and from patient to patient.
Some studies analyzed the lymphatic drainage seen in cutaneous melanoma at different levels(7,8,9,10).
Fig 2-9.
Region |
Where to look sentinel lymph nodes |
Ear,
face,
anterior scalp |
Parotid nodes,
postauricular nodes,
nodes at the base of the neck (levels I–V),
supraclavicular nodes,
axillary nodes. |
Posterior scalp,
occipital skin |
Postauricular nodes,
parotid nodes,
nodes at the base of the neck (especially level II–V),
supraclavicular nodes,
axillary nodes. |
Anterior trunk |
Above umbilicus: supraclavicular fossa,
axillary nodes,
nodes at the base of the neck,
costal margin,
internal mammary,
groin.
Below umbilicus: Groin,
axillary nodes |
Posterior trunk |
Above waist: axillary nodes,
groin,
triangular intermuscular space,
cervical,
occipital,
supraclavicular,
postauricular,
paravertebral,
para-aortic,
retroperitoneal.
Below waist: axillary nodes,
groin,
paravertebral,
para-aortic,
retroperitoneal. |
Upper limb |
Axillary nodes,
epitrochlear,
cervical (level V),
supraclavicular,
triangular intermuscular space,
interpectoral,
infraclavicular. |
Lower limb |
Groin,
popliteal,
iliac obturator nodes. |
Sentinel nodes in the paravertebral,
para-aortic,
and retroperitoneal areas represent locoregional metastasis,
not a systemic disease (7).
The sentinel node is not always found in the nearest node field and is best defined as “any lymph node receiving direct lymphatic drainage from a primary tumor site.”
Drainage across the midline of the body is quite common in the trunk and in the head and neck. Drainage to the contralateral nodes is almost not seen at limbs(9).
TNM 8 and Staging.
Fig 10 and Fig 11.