Skin Tumor Imaging

Skin is the largest organ in the human body, harboring the most common type of cancers in the United States. Skin and subcutaneous malignancies are commonly detected during routine imaging studies, either as a known entity or an incidental finding. Even though clinically significant, sometimes these lesions are located on the edge of images and can be easily missed. Epithelial malignancies represent the most common skin malignancies, with basal cell carcinoma being the most common, followed by squamous cell carcinoma and melanoma. Cutaneous and subcutaneous mesenchymal malignancies are rare, with dermatofibrosarcoma protuberans (DFSP), leiomyosarcoma, liposarcoma, and angiosarcoma being more commonly reported, whereas Kaposi sarcoma and desmoid tumors are rare.Histopathology remains the reference standard for the diagnosis of skin malignancies. The anatomic imaging techniques available for assessing skin cancers include laser scanning confocal microscopy, optical coherence tomography, high-frequency ultrasound, terahertz pulsed imaging, CT, MRI, and 18F-FDG PET. A discussion of confocal microscopy, optical coherence tomography, and high-frequency ultrasound is beyond the scope of this article. Noninvasive imaging techniques, such as CT, MRI, and PET/CT, aid in baseline tumor staging, preoperative planning, and assessment of response to treatment. Of these, CT is the least expensive, with wide availability, and it aids in delineating tumor extent, staging, and follow-up, with a significant role in the evaluation of pulmonary metastases. MRI provides high Spatial and contrast resolution imaging of the skin. PET/CT provides both morphologic information and data on tumor metabolic activity; it can also unmask subtle recurrences, micrometastases, and indeterminate nodal metastases resulting from various skin malignancies. This lecture aims to enlighten clinicians with multimodality imaging features, patterns of local recurrence and distant spread, differential diagnosis, and prognosis of the primary and secondary neoplasms involving the skin and subcutaneous tissues. Increased awareness of these entities will help to optimize care of patients with cancer.