Imaging Work-up of the Patient with Melanoma

Key Points

Imaging is heavily utilized in the diagnosis and management of melanoma patients but the utility of imaging depends upon the goal in the context of the clinical disease setting.
For staging purposes, little evidence supports comprehensive body imaging assessment in asymptomatic early-stage melanoma patients.
High-frequency ultrasound can augment the sensitivity of sentinel lymph node biopsy assessment of regional nodal disease.
Routine follow-up of melanoma with chest X-ray has not been validated in rigorous studies to date.
There is no current role for radiologic surveillance, and no rationale for performance of baseline PET or PET/CT studies in stage IIB or III patients.
Contrast-enhanced MRI is the most sensitive modality for detecting brain metastasis.

Introduction

The utility of radiologic imaging at different junctures in the evaluation and management of patients with melanoma continues to increase. With higher-risk deep primary melanoma and melanoma that has spread to regional nodes, surgery with adjuvant therapy reduces local-regional and distant recurrence and the outcome is linked to disease burden. Microscopic nodal disease has a substantially better outcome than gross nodal disease. Imaging technology has evolved rapidly in the past two decades, providing us with new tools to assess the burden of metastatic disease. Imaging at the time of diagnosis of melanoma and for subsequent surveillance plays an important role in management.

Imaging at diagnosis

The staging of localized primary melanoma is dictated by the microstage (thickness, ulceration, and mitotic index) of the primary lesion. Melanoma metastasis occurs locally through the skin, regionally through the lymphatics, and systemically by hematogenous routes. Sentinel lymph node biopsy (SLNB) is an essential component of staging to be considered for primary melanomas >1 mm Breslow thickness or any primary melanoma with ulceration. Initial staging can employ various imaging modalities, including chest X-ray (CXR), regional nodal ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and combined (co-registered) PET/CT.

Chest X-ray (CXR)

Hematogenous dissemination is the third major route of metastasis for melanoma, most commonly afflicting the lung. Modern chest radiography requires small doses of radiation, and is quick, inexpensive, and relatively easy to perform. It therefore seems reasonable as a means to assess the lungs for metastasis although multiple studies have indicated a very low yield for CXR as part of the initial work-up.

In 876 asymptomatic patients with localized melanoma, Terhune et al. found that only 15% had suspicious findings on CXR and only one patient had metastatic melanoma confirmed by biopsy, for a yield of only 0.1%. A similar yield of 0.2% was reported in a study of 524 stage I and II patients, with a sobering 20-fold higher false positive (FP) rate (4.4%). A high FP rate serves to further increase patient anxiety and reduce overall cost-effectiveness.

Yancovitz et al. reported retrospectively on 158 asymptomatic patients with T1b–T3b primary lesions, clinically N0. A total of 344 preoperative imaging studies (CXR, CT, and PET/CT) were performed, resulting in 49 findings suspicious for metastatic melanoma. Only 1 of 344 studies correlated with confirmed metastatic melanoma. No patient was upstaged or had a change in initial surgical management based on preoperative imaging. In addition, no survival benefit from CXR at initial staging or during follow-up has been demonstrated.

These findings suggest that chest radiography of asymptomatic patients at the time of diagnosis may not be warranted. However, obtaining a chest radiograph in a symptomatic patient or at an advanced T-or N-stage may be reasonable.

Ultrasound

Ultrasound is a non-invasive, low-cost, portable investigation. It carries a lower risk to patients, given the absence of ionizing radiation. Ultrasound has been used for imaging of skin lesions, abdominal and pelvic organs and staging of regional nodes.

Harland et al. reported 100% sensitivity in distinguishing between basal cell carcinoma and malignant melanoma. Similar sensitivity and specificity (100%) for melanoma were reported in 111 patients among whom 81% of melanomas were correctly identified.

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