Positron Emission Tomography/Computed Tomography Transformation of Oncology: Melanoma and Skin Malignancies

Skin cancers are the most common cancers, with melanoma resulting in the highest cause of death in this category. Accurate clinical, histologic, and imaging staging with fludeoxyglucose positron emission tomography (FDG PET) is most important to guide patient management. Whilst surgical excision with clear margins is the gold-standard treatment for primary cutaneous melanoma, targeted therapies have generated remarkable and rapid clinical responses in melanoma, for which FDG PET also plays an important role in assessment of treatment response and post-therapy surveillance. Non-FDG PET tracers, advanced PET technology, and PET radiomics may potentially change the landscape of the utilization of PET in the imaging of patients with cutaneous malignancies.

Skin Malignancies: Imaging Review with Radiologic-Histopathologic Correlation

Skin malignancies are commonly encountered as primary or incidental findings. Neoplasms that affect the skin include primary (basal cell carcinoma, squamous cell carcinoma, melanoma, and Merkel cell carcinoma) and secondary (mesenchymal neoplasms, lymphoma, and metastases) tumors. Imaging provides valuable anatomic information (tumor size, depth of involvement, presence of distant metastasis, and data for guiding biopsy) and functional information (metabolic activity and sentinel node mapping data). This information, in addition to biopsy results, improves the histopathologic characterization of tumors and treatment planning. Various histopathologic types of the same entity exhibit different biologic behavior and have different imaging features. Familiarity with the multimodality imaging features, histopathologic characteristics, and various modes of dissemination (direct invasion; perineural, lymphatic, and hematogenous spread) of the most common skin malignancies helps radiologists narrow the differential diagnosis in clinical practice. ©RSNA, 2023 Supplemental material is available for this article. Quiz questions for this article are available through the Online Learning Center.

Rare Primary Malignant Melanoma of the Breast Presenting as a Solitary Breast Mass in a 43-Year-Old Male

Primary malignant melanoma of the breast (PMMB) is an extremely rare lesion that carries a poor prognosis. Therefore, it is crucial to examine the patient's medical history, clinical presentation, and histopathology considering this diagnosis. The rarity of this lesion has made it difficult to identify classic presentations or specific treatment guidelines. Staining for specific biomarkers can be helpful for diagnosis in the absence of melanin pigment on histology. Additional molecular studies to determine gene status can also be useful for targeted immunotherapy and increased survival time for patients. In this paper, we introduce a rare case of PMMB without skin involvement presenting as a solitary breast mass in a male and explore the radiology, histology, evaluation, and treatment options.

Review of primary superficial soft tissue mesenchymal tumors of malignant or intermediate biological potential

The majority of the sarcomas are deep in location, larger than 5 cm in size, and heterogenous in imaging appearance. However, when sarcomas occur superficially, these typical features may be absent, failing to alert the radiologist to a malignancy and mimicking one of the more numerous benign superficial tumors that make up the bulk of soft tissue mass evaluations. This manuscript will discuss the current role of imaging in recognizing features concerning for superficial soft tissue sarcomas. Provided is an overview of the demographic, clinical, and imaging features of the most commonly encountered superficial soft tissue sarcomas, including undifferentiated pleomorphic, leiomyosarcoma, synovial sarcoma, liposarcoma, myxofibrosarcoma, dermatofibrosarcoma protuberans, epithelioid sarcoma, and angiosarcoma. A less common but primary superficial tumor, angiomatoid fibrous histiocytoma, is also reviewed as the diagnosis may be confounding both clinically and on imaging studies.

Management of Non-Melanoma Skin Cancer: Radiologists Challenging and Risk Assessment

Basal cell carcinoma, squamous cell carcinoma, and Merkel cell carcinoma are the three main types of nonmelanoma skin cancers and their rates of occurrence and mortality have been steadily rising over the past few decades. For radiologists, it is still difficult to treat patients with advanced nonmelanoma skin cancer. Nonmelanoma skin cancer patients would benefit greatly from an improved diagnostic imaging-based risk stratification and staging method that takes into account patient characteristics. The risk is especially elevated among those who previously received systemic treatment or phototherapy. Systemic treatments, including biologic therapies and methotrexate (MTX), are effective in managing immune-mediated diseases; however, they may increase susceptibility to NMSC due to immunosuppression or other factors. Risk stratification and staging tools are crucial in treatment planning and prognostic evaluation. PET/CT appears more sensitive and superior to CT and MRI for nodal and distant metastasis as well as in surveillance after surgery. The patient treatment response improved with advent and utilization of immunotherapy and different immune-specific criteria are established to standardized evaluation criteria of clinical trials but none of them have been utilized routinely with immunotherapy. The advent of immunotherapy has also arisen new critical issues for radiologists, such as atypical response pattern, pseudo-progression, as well as immune-related adverse events that require early identification to optimize and improve patient prognosis and management. It is important for radiologists to have knowledge of the radiologic features site of the tumor, clinical stage, histological subtype, and any high-risk features to assess immunotherapy treatment response and immune-related adverse events.

Nonbrain metastases seen on magnetic resonance imaging during metastatic brain tumor screening

Although metastases found during head magnetic resonance imaging (MRI) are not limited to metastatic brain tumors, the MRI is a very common method for “brain metastasis screening,” a modality that is being increasingly performed. In this review, we describe MRI findings of nonbrain metastases and discuss ways to avoid missing these lesions. Metastatic cranial bone tumors are among the most common nonbrain metastatic lesions found on head MRI, followed by leptomeningeal carcinomatosis. The other less-frequent metastatic lesions include those in the ventricle/choroid plexus, the pituitary gland and stalk, and the pineal gland. Metastases in the head and neck area, as well as cranial and intracranial lesions, should be carefully evaluated. Furthermore, direct geographical invasion, perineural spread, and double cancers should also be considered. While it is important to recognize these metastatic lesions on MRI, because they may necessitate a change in treatment strategy that could lead to an improvement in prognosis due to early introduction of therapy, nonbrain lesions should also be given greater attention, given the increasing survival of patients with cancer and advances in MRI technology, such as contrast-enhanced-3D T1-weighted imaging.

MRI techniques for immunotherapy monitoring

MRI is a widely available clinical tool for cancer diagnosis and treatment monitoring. MRI provides excellent soft tissue imaging, using a wide range of contrast mechanisms, and can non-invasively detect tissue metabolites. These approaches can be used to distinguish cancer from normal tissues, to stratify tumor aggressiveness, and to identify changes within both the tumor and its microenvironment in response to therapy. In this review, the role of MRI in immunotherapy monitoring will be discussed and how it could be utilized in the future to address some of the unique clinical questions that arise from immunotherapy. For example, MRI could play a role in identifying pseudoprogression, mixed response, T cell infiltration, cell tracking, and some of the characteristic immune-related adverse events associated with these agents. The factors to be considered when developing MRI imaging biomarkers for immunotherapy will be reviewed. Finally, the advantages and limitations of each approach will be discussed, as well as the challenges for future clinical translation into routine clinical care. Given the increasing use of immunotherapy in a wide range of cancers and the ability of MRI to detect the microstructural and functional changes associated with successful response to immunotherapy, the technique has great potential for more widespread and routine use in the future for these applications.

Left Forearm Langerhans Cell Sarcoma Demonstrated by 18F-FDG PET/CT

ABSTRACT

Langerhans cell sarcoma is a rare neoplastic proliferation of Langerhans cells with a poor prognosis. We report FDG PET/CT findings of Langerhans cell sarcoma in the left forearm of a 77-year-old woman who presented with progressive enlargement of the left forearm mass for over 2 months. 18F-FDG PET/CT demonstrated a high FDG uptake by the mass along with several FDG-avid enlarged lymph nodes in the left arm and axilla. Pathology examination of the biopsied specimen from the left forearm mass led to a diagnosis of Langerhans cell sarcoma.

Imaging findings of malignant skin tumors: radiological-pathological correlation

Sometimes, radiologists encounter malignant skin tumors (MSTs) during image interpretation. As MSTs require different clinical management modalities for each histological subtype, accurate preoperative diagnosis is essential. The histological subtypes of MST can be easily assessed by visual inspection or biopsy. Therefore, the significant role of radiological imaging in MSTs is to evaluate the extent of local invasion, nodal involvement, and distant metastasis, and the histological estimation of MSTs by radiological imaging has not been reported until a few years ago. However, recent studies have revealed characteristic radiological features for differential diagnosis of MSTs, such as configuration, intratumoral homogeneity, signal intensity, cyst formation, and hemorrhage. Other important clinical data for determining the histological subtype of MST include age, gender, and site of occurrence. MSTs can be categorized as epidermal, melanocytic, adnexal, and mesenchymal tumors based on the origin and have distinctive characteristics. Hence, this review article was designed to describe the clinical and radiological features of MSTs.

Imaging features of primary sites and metastatic patterns of angiosarcoma

Angiosarcomas are rare, aggressive soft tissue sarcomas originating from endothelial cells of lymphatic or vascular origin and associated with a poor prognosis. The clinical and imaging features of angiosarcomas are heterogeneous with a wide spectrum of findings involving any site of the body, but these most commonly present as cutaneous disease in the head and neck of elderly men. MRI and CT are complementary imaging techniques in assessing the extent of disease, focality and involvement of adjacent anatomical structures at the primary site of disease. CT plays an important role in the evaluation of metastatic disease. Given the wide range of imaging findings, correlation with clinical findings, specific risk factors and patterns of metastatic disease can help narrow the differential diagnosis. The final diagnosis should be confirmed with histopathology and immunohistochemistry in combination with clinical and imaging findings in a multidisciplinary setting with specialist sarcoma expertise. The purpose of this review is to describe the clinical and imaging features of primary sites and metastatic patterns of angiosarcomas utilising CT and MRI.

The differential diagnosis of trunk and extremity dermal and sub-dermal lesions referred to a musculoskeletal oncology service

OBJECTIVES

To determine the differential diagnosis of dermal and sub-dermal soft tissue masses which do not extend to the deep fascia that are referred to a specialist musculoskeletal oncology service.

MATERIALS AND METHODS

Review of all patients referred to a specialist musculoskeletal oncology service over a 13-month period with a dermal or sub-dermal soft tissue mass which did not extend to the deep fascia based on MRI appearances. Data collected included age, gender, site and maximal lesion size, and final histological diagnosis for biopsied and/or excised lesions.

RESULTS

56 patients were included, 21 (37.5%) males and 35 (62.5%) females with mean age 49.75 years (range 5-86 years). 3 patients had 2 lesions making a total of 59 lesions, 11 (18.6%) dermal and 48 (81.4%) sub-dermal. Histological diagnosis was available in 44 (74.6%) cases, of which 11 (25%) were non-neoplastic, 23 (52.3%) were benign neoplasms, and 10 (22.7%) were malignant neoplasms. Although older age at presentation and greater mean maximal tumour dimension were seen with malignant lesions, these did not reach statistical significance (p = 0.154 and 0.102 respectively). There was also no relationship between skin involvement from sub-dermal lesions and malignancy, but 5 of 6 dermal lesions which showed an exophytic growth pattern were malignant.

CONCLUSIONS

The differential diagnosis of dermal and sub-dermal lesions which do not reach the deep fascia is wide with a malignant lesion being the cause in almost one-quarter of cases.

Radiogenomics and Its Role in Lymphoma

PURPOSE OF REVIEW

Imaging features of lymphoma vary regionally. Awareness of site-specific key imaging characteristics of lymphoma can aid in rapid staging and assist in prompt treatment. FDG PET/CT and conventional MRI are readily available diagnostic modalities with excellent sensitivity and good specificity. Diagnostic specificity can be enhanced using emerging PET radiotracers, e.g., FLT and FET.

RECENT FINDINGS

Emerging research has shown higher dimensional analysis (radiomics and radiogenomics) of imaging data can yield information of the underlying genetic aberrations in lymphoma, which can aid in assessing real-time evolution of tumor. CT, PET/CT, MRI, and ultrasound accentuate the intrinsic qualities of lymphoma (e.g., FDG PET/CT for increased metabolic activity, FLT PET/CT for increased proliferation index, and DWI for increased cellularity) and play an essential role in its diagnosis and examination. Advanced radiogenomic analyses use radiomic parameters to deduce genetic variations of lymphoma, providing noninvasive, repeatable, and real-time surveillance of its genetic progression.

Small Subcutaneous Soft Tissue Tumors (<5 cm) Can Be Sarcomas and Contrast-Enhanced Ultrasound (CEUS) Is Useful to Identify Potentially Malignant Masses

Subcutaneous masses smaller than 5 cm can be malignant, in contrast with the international guidelines. Ultrasound (US) and magnetic resonance imaging (MRI) are useful to distinguish a potentially malignant mass from the numerous benign soft tissue (ST) lesions. Contrast-enhanced ultrasound (CEUS) was applied in ST tumors, without distinguishing the subcutaneous from the deep lesions. We evaluated CEUS and MRI accuracy in comparison to histology in differentiating malignant from nonmalignant superficial ST masses, 50% smaller than 5 cm. Sensitivity, specificity, and positive and negative predictive values (PPV, NPV) with their 95% confidence intervals (CI) were calculated. Of malignant cases, 44.4% measured ≤5 cm. At univariate analysis, no statistically significant differences emerged between benign and malignant tumors in relation with clinical characteristics, except for relationship with the deep fascia (p = 0.048). MRI accuracy: sensitivity 52.8% (CI 37.0, 68.0), specificity 74.1% (CI 55.3, 86.8), PPV 73.1% (CI 53.9, 86.3), and NPV 54.1% (CI 38.4, 69.0). CEUS accuracy: sensitivity 75% (CI 58.9, 86.3), specificity 37% (CI 21.5, 55.8), PPV 61.4% (CI 46.6, 74.3), and NPV 52.6% (CI 31.7, 72.7). CEUS showed a sensitivity higher than MRI, whereas PPV and NPV were comparable. Also, masses measuring less than 5 cm can be malignant and referral criteria for centralization could be revised.

Imaging Features of Neurofibromatosis Type 1 in the Abdomen and Pelvis

OBJECTIVE. Loss of the neurofibromatosis type 1 (NF1) tumor suppressor protein causes uninhibited activation of the RAS oncogene, which leads to tumorigenesis in patients with NF1. This case-based review discusses imaging manifestations of NF1 in the abdomen and pelvis, highlighting key genetic associations and management to elucidate features different from the general population. CONCLUSION. The spectrum of pathologic findings includes gastrointestinal tumors such as gastrointestinal stromal tumors, genitourinary lesions including urogenital neurofibromas, vascular entities such as renal artery stenosis, and less common associations like lymphoma.

Magnetic Resonance Imaging Findings Differentiating Cutaneous Basal Cell Carcinoma from Squamous Cell Carcinoma in the Head and Neck Region

Objective

This study aimed to evaluate the efficacy of magnetic resonance (MR) imaging in differentiating between cutaneous basal cell carcinoma (cBCC) and cutaneous squamous cell carcinoma (cSCC) in the head and neck region.

Materials and Methods

Among patients with cutaneous head and neck cancers, 14 with primary cBCCs and 15 with primary cSCCs with a histologic tumor height of ≥ 4 mm underwent MR examinations; the findings were then examined for correlations.

Results

cBCCs (71%) occurred more frequently on the nose than cSCCs (13%) (p < 0.01). The maximum diameter (23.5 ± 7.2 mm vs. 12.7 ± 4.5 mm; p < 0.01) and diameter-to-height ratio (2.8 ± 0.9 vs. 1.7 ± 0.4; p < 0.01) were significantly greater in cSCCs than in cBCCs. Superficial ulcer formation (67% vs. 21%; p < 0.05), protrusion into the subcutaneous tissue (60% vs. 21%; p < 0.05), ill-demarcated deep tumor margins (60% vs. 7%; p < 0.01), and peritumoral fat stranding (93% vs. 7%; p < 0.01) were more frequently observed in cSCCs than in cBCCs. Intratumoral T2-hyperintense foci (57% vs. 13%; p < 0.05) were more frequently observed in cBCCs than in cSCCs.

Conclusion

cBCCs predominantly occurred on the nose with intratumoral T2-hyperintense foci, whereas cSCCs predominantly exhibited a flattened configuration, superficial ulcer formation, protrusion into the subcutaneous tissue, ill-demarcated deep tumor margin, and peritumoral fat stranding.

Imaging of Abdominal Wall Masses, Masslike Lesions, and Diffuse Processes

Abdominal wall masses, masslike lesions, and diffuse processes are common and often incidental findings at cross-sectional imaging. Distinguishing among these types of masses on the basis of imaging features alone can be challenging. The authors present a diagnostic algorithm that may help in distinguishing different types of abdominal wall masses accurately. Hernias may mimic discrete masses at clinical examination, and imaging is often ordered for evaluation of a possible abdominal wall mass. Once a discrete mass is confirmed to be present, the next step is to determine if it is a fat-containing, cystic, or solid mass. The most common fat-containing masses are lipomas. Fluid or cystic masses include postoperative abscesses, seromas, and rectus sheath hematomas. Solid masses are the most common abdominal wall masses and include desmoid tumors, sarcomas, endometriomas, and metastases. Multiple masses and other diffuse abdominal wall processes are often manifestations of an underlying condition or insult. The most frequently found diffuse processes are multiple injection granulomas from administration of subcutaneous medication. This article offers an algorithmic approach to characterizing abdominal wall masses on the basis of their composition and reviews abdominal wall diffuse processes. Online supplemental material is available for this article. ^©RSNA, 2020.

Clinical value of FDG-PET/CT in bacteremia of unknown origin with catalase-negative gram-positive cocci or Staphylococcus aureus

INTRODUCTION

Bacteremia is associated with high mortality, especially when the site of infection is unknown. While conventional imaging usually focus on specific body parts, FDG-PET/CT visualizes hypermetabolic foci throughout the body.

PURPOSE

To investigate the ability of FDG/PET-CT to detect the site of infection and its clinical impact in bacteremia of unknown origin with catalase-negative Gram-positive cocci (excluding pneumococci and enterococci) or Staphylococcus aureus (BUOCSA).

METHODS

We retrospectively identified 157 patients with 165 episodes of BUOCSA, who subsequently underwent FDG-PET/CT. Data were collected from medical records. Decision regarding important sites of infection in patients with bacteremia was based on the entire patient course and served as reference diagnosis for comparison with FDG-PET/CT findings. FDG-PET/CT was considered to have high clinical impact if it correctly revealed site(s) of infection in areas not assessed by other imaging modalities or if other imaging modalities were negative/equivocal in these areas, or if it established a new clinically relevant diagnosis, and/or led to change in antimicrobial treatment.

RESULTS

FDG-PET/CT detected sites of infection in 56.4% of cases and had high clinical impact in 47.3%. It was the first imaging modality to identify sites of infection in 41.1% bacteremia cases, led to change of antimicrobial therapy in 14.7%, and established a new diagnosis unrelated to bacteremia in 9.8%. Detection rate and clinical impact were not significantly influenced by duration of antimicrobial treatment preceding FDG-PET/CT, days from suspicion of bacteremia to FDG-PET/CT-scan, type of bacteremia, or cancer.

CONCLUSION

FDG-PET/CT appears clinically useful in BUOCSA. Prospective studies are warranted for confirmation.

The skinny on skin: MRI features of cutaneous and subcutaneous lesions detected on body MRI studies

The skin and subcutaneous tissues are inevitably imaged as part of most body MRI studies. Incidental or even symptomatic skin lesions may, therefore, be detected and present a diagnostic challenge for the radiologist. We aim to provide a comprehensive review, with illustrative examples, of the skin abnormalities encountered on body MRI studies in our busy academic radiology department.

FDG-Avid Keloid on PET/CT Imaging

Keloid is a benign fibroproliferative growths resulting from an overexuberant healing response. A 51-year-old man with a 20-year history of keloid formation presented with a 1-year history of unexplained progressive weakness of both lower limbs. He was clinically suspected of having paraneoplastic neurologic syndrome. FDG PET/CT was performed to exclude underlying malignancy. FDG PET/CT revealed a giant FDG-avid keloid in the anterior chest wall without any other abnormal FDG uptake in the body. We emphasize that a benign FDG-avid keloid should be considered in the differential diagnosis of FDG-avid cutaneous lesions on PET/CT.

Imaging analysis of superficial soft tissue lymphomas

PURPOSE

To describe imaging findings in superficial soft tissue lymphomas, especially those located in the skin and subcutaneous layer.

MATERIALS AND METHODS

This study included 44 pathologically confirmed superficial lymphoma lesions. Imaging analysis included the size, margin, location, morphology, homogeneity and multiplicity.

RESULTS

A nodular form was the most common (21/44, 47.7%) morphology, and of them, 18 demonstrated a streaky appearance. Most of the lesions demonstrated ill-defined margins (26/44, 59.1%) and homogeneous patterns (35/44, 79.5%).

CONCLUSIONS

The imaging findings of superficial soft tissue lymphomas were non-specific. However, if images show multiple nodular lesions with ill-defined margins, we should consider this diagnosis.

Bilateral multifocal lower extremity localized soft tissue amyloidomas: case report with ultrasonographic characterization

Amyloidosis may be acquired or hereditary and consists of multiple disease processes characterized by the abnormal deposition of extracellular fibrillary protein aggregates. The presentation of amyloidosis is varied, ranging from an isolated, focal deposition to systemic disease. While systemic involvement is common, a rare entity known as amyloidoma or tumor amyloidosis may also occur. The 75-year-old female in this case presented with slowly growing multifocal bilateral lower extremity masses and was ultimately diagnosed with localized amyloidomas in the absence of chronic illness or systemic disease. This case report includes a description of the sonographic features of localized extremity amyloidoma that, to the best of our knowledge, have not yet been described in the literature. Awareness of the sonographic features, and this unique presentation of multifocal soft tissue extremity amyloidomas will allow for this rare diagnosis to be included in a limited differential diagnosis.

Blastic Plasmacytoid Dendritic Cell Neoplasm Evaluated by FDG PET/CT

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematological malignancy. A 34-year-old man with a biopsy-proven BPDCN underwent FDG PET/CT for staging. FDG PET/CT revealed multiple mild FDG-avid cutaneous lesions on the chest and back, involvement of left inguinal lymph node, and a markedly increased FDG-avid subcutaneous mass in the left lower leg.

Dramatic treatment response of cutaneous plasmablastic lymphoma in an HIV patient: a case report

Plasmablastic lymphoma is a variant of diffuse large B-cell lymphoma, characterized by rapid progression and is associated with a poor outcome. We report a 35-year-old male with poorly controlled HIV infection and AIDS who presented with skin lesions and swelling throughout the body. Computed tomography (CT) revealed innumerable enhancing soft tissue masses within the subcutaneous soft tissues and lymphadenopathy. Plasmablastic lymphoma was diagnosed, patient was treated with chemotherapy, and post treatment CT demonstrated complete resolution. Imaging plays a key role in the diagnosis and surveillance of this disease.

The utility of positron emission tomography with and without computed tomography in patients with nonmelanoma skin cancer

Combined positron emission tomography (PET) and computed tomography (CT) scans are widely used in the staging and monitoring of most malignancies. The differential for PET-positive cutaneous lesions includes primary skin cancers, infections, cutaneous metastases from distant malignancies, and benign neoplasms. In dermatology, PET/CT scans have been most widely studied in patients with melanoma and Merkel cell carcinoma. The role of PET/CT scans in the management of other cutaneous malignancies is less clear, but it has shown great promise in the management of patients with squamous cell carcinoma and cutaneous lymphoma. This review seeks to address the usefulness of PET/CT scans in nonmelanoma skin cancer and to provide guidance regarding the management of patients with incidental PET-positive nodules. Currently, there is limited experience with PET/CT scans for staging and monitoring of non-head and neck metastatic basal cell and squamous cell carcinomas, and results show limited sensitivity and specificity. We also address the evidence for management of an incidental PET-positive cutaneous nodule and recommend obtaining a biopsy specimen in patients with a known noncutaneous malignancy, a history of primary skin cancer, or a high risk of either cutaneous or noncutaneous malignancy.