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Looking to the subcutaneous tissue Poster No.: C-2357 Congress: ECR 2010 Type: Educational Exhibit Topic: Musculoskeletal Authors: G. Garrido , J. Andreu , E. Herrera-Acosta , A. Roque , D. 1 1 1 1 2 1 1 1 2 Varona , O. Persiva , J. Cáceres ; Barcelona/ES, Málaga/ES Keywords: Subcutaneous tissue, Multidetector computed tomography, Thoracoabdominal wall DOI: 10.1594/ecr2010/C-2357 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. 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Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myESR.org Page 1 of 33 Learning objectives 1.To review the anatomy, histopathology and normal multidetector computed tomography (MDCT) imaging appearance of the thoracoabdominal subcutaneous tissue (ST), excluding the breast and, the axillar and inguinal regions. 2.To illustrate the broad spectrum of lesions arising from or extending into the subcutaneous tissue. 3.To discuss the differential diagnoses and its impact on patient management. Background The subcutaneous tissue is an anatomical space often ignored by radiologists. Incidental findings are common and usually irrelevant but, occasionally these findings can be related to serious diseases. We reviewed the imaging findings of patients with subcutaneous tissue anomalies from our database of oncologic CT department. All the examinations were performed on a 64-slice MDCT unit and consisted in contrastenhanced chest and abdominal MDCT scan from the thoracic inlet to the pubic symphysis This educational exhibit is based on our experience. It is not intended as a comprehensive review but, rather, as an overview, with emphases on lesions that are more common or relatively more common and on diagnoses that may be suggested by MDCT imaging findings. Anatomy, histopathology and MDCT imaging Page 2 of 33 The subcutaneous fat is widely scattered throughout the body. The thickness of the subcutis varies with the sex, nutritional status of the individual and anatomic location. Fig.: Variability of the subcutaneous adipose layer thickness: thin (left)/thick (right) References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN The subcutis or subcutaneous tissue represents the deepest layer of the skin, located below the epidermis and the dermis. Traversing the dermis and the subcutis are the peripheral branches of the vascular and nervous systems, as well as epidermal appendages. Below the subcutis, fascia is found. Fig.: Anatomy and MDCT imaging References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Page 3 of 33 The subcutaneous fat is composed of lobules of adipocytes or lipocytes separated by fibrous connective-tissue septa. Arteries and veins of the subcutis as well as nerves run along these septa. A rich lymphatic plexus is also contained into the septa, coming from the dermis and traversing the subcutis, first parallel to the surface of the skin and then vertically penetrating the deep fascia and draining into the regional lymph nodes. Fig.: Histopathology References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Imaging findings OR Procedure details Pathological conditions affecting the subcutaneous tissue have been divided into: •Benign and malignant nodules-masses •Inflammatory-infectious conditions •Foreign bodies and subcutaneous tissue occupation Page 4 of 33 Benign and malignant nodules-masses Benign nodules-masses The benign nodules-masses, including tumor and tumor-like lesions, that can be encountered in the subcutaneous tissue include: •Epidermoid cysts •Lipomas •Neural tumors •Vascular lesions (hemangiomas, hematomas, collateral vessels) Epidermoid cyst Epidermoid cysts represent the most common cutaneous cysts. They are derived from the epithelium of the hair follicles and consist in cysts filled with keratin and bounded by a wall of stratified squamous epithelium. They are usually located at or just below the skin (metastasis may be distant from the skin) and may be large enough to protrude into the subcutis. Epidermoid cyst attenuation is similar to that of skeletal muscle on CT images with no enhancement after contrast material administration. Fig.: Epidermoid cyst References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Lipoma Page 5 of 33 Lipomas are the most frequently encountered subcutaneous masses. They are benign subcutaneous tumors composed of fat cells. At CT, lipomas usually have a smooth border, are well marginated and demonstrate homogeneous fatty attenuation values (-100 to -160 HU). A significant number of lipomas have prominent non-adipose areas, difficulting its differentiation with low grade liposarcomas. Features favoring the diagnosis of well-differentiated liposarcoma include lesion size greater than 10cm, presence of thick (>2mm) septa (diffuse or focal), presence of nodular and/or globular nonadipose areas or masses, and lesion composition of less than 75% of fat. Lipomas can not always be successfully distinguished from well-differentiated liposarcoma on the basis of CT imaging alone. Fig.: Lipoma References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Neural tumors: Benign peripheral nerve sheath tumors are divided into two major categories: neurofibroma and schwannoma. Page 6 of 33 Although major nerve trunks are most commonly affected, virtually any peripheral nerve can represent a site of origin. Since both neoplams, deep or superficially located, have CT imaging findings closely similar, that in most cases don't allow their distinction, multiple clinical and pathologic features have to be considered to make an accurate diagnosis. Neurofibromas: Three type of neurofibromas are classically described: localized, diffuse and plexiform (pathognomonic for NF1). -The localized neurofibroma is the most common (~90%), usually solitary and not associated with NF1. Localized neurofibromas often involve small cutaneous nerves and are typically small painless masses. CT of superficial localized neurofibromas shows a well defined mass, hypodense relative to muscle and enhancing after contrast administration. The typical fusiform morphology seen in deep lesions, that represent the entering and exiting nerve, is often difficult or impossible to identify. -Diffuse neurofibromas primarily affects children and young adults and most frequently involves the subcutaneous tissue of the head and neck. Most of them are isolated lesions not associated with NF1. Diffuse neurofibromas show a reticulated, linear branching pattern within the subcutaneous tissue, replacing the fat and creating a honeycomb appearance. -Neurofibromatosis type1 (NF1): Is the most common of the phakomatosis and has a wide spectrum of clinical expression with neurocutaneous abnormalities and involvement of multiple organ systems. All three type of neurofibromas can be associated with NF1, beeing the localized neurofibroma the most common type. Localized neurofibromas associated with NF1 more commonly involve large deep nerves, are large in size and multiple in number. They often affect the dermis and subcutaneous tissue. Plexiform neurofibromas are pathognomonic of NF1 and, development of these lesions usually occurs in early childhood and precedes cutaneous neurofibromas. Plexiform neurofibromas show a pathognomonic imaging appearance identical to their gross pathologic features of diffuse nerve thickening. There is often nodularity and involvement of nerve branches, which creates the appearance of a serpentine "bag of worms". Page 7 of 33 Fig.: Neurofibromatosis 1. Cutaneous and subcutaneous neurofibromas. References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Vascular lesions: Angiomatous lesions Angiomatous lesions (hemangiomas and vascular malformations) are a common disorder, multiple in as many as 20% of patients. They usually are very characteristic, being inhomogeneous, well defined and smooth bordered, containing round calcific densities (phleboliths) and enhancing after contrast administration. If deep enough, underlying bone remodelling can be seen. Vascular neoplasms typically have dilated tortuous vessels entering and/or exiting the lesion and include hemangiomas, lymphangiomas, and angiosarcomas. Page 8 of 33 Fig.: Subcutaneous hemangioma References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Collateral vessels Collateral vessels in the subcutaneous tissue are often an indication of underlying venous obstruction. Subcutaneous vessels may simulate a nodule on a single axial image, but they can be identified on contiguous cuts and have marked enhancement after contrast administration. Page 9 of 33 Fig.: Collateral vessels within the subcutaneous tissue. References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Hematomas Occurring after a traumatic event or in patients who are receiving anticoagulant treatment or who have a clotting deficiency. Subcutaneous hematomas are rarely associated to underlying tumors. They usually appear as areas of high density in unenhanced or enhanced CT. Hematomas that do not resolve may calcify peripherally or may continue to bleed, forming a chronic expanding hematoma. Page 10 of 33 Fig.: Hematoma References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Malignant nodules-masses Malignant nodules-masses that can be found within the subcutaneous tissue include: •Primary soft tissue sarcomas (rare) •Primary peripheral T-cell lymphoma (rare) •Secondary malignancies •Metastases •Extension from adjacent malignancies Secondary malignancies-Metastases Cutaneous metastases from carcinoma are relatively uncommon in clinical practice, but they are very important to recognize. The breast, stomach, lung, uterus, large intestine, and kidneys are the most frequent organs to produce cutaneous metastases. Cancers that have the highest propensity to metastasize to the skin include melanoma (45% of cutaneous metastasis cases), breast (30%), nasal sinuses (20%), larynx (16%), and oral cavity (12%). Page 11 of 33 Different pathways may be involved in the metastatic process: lymphatic and hematogenous spreads are the most common. Extension can also be produced through serosal surfaces or perineurium, or by surgical implantation. At CT examinations, subcutaneous metastasis should always be suspected when multiple nodules are found. In cancer patients, a new-appearing solitary nodule or its progressive enlargement may also be suspicious. Homogeneous or rim enhancement may be found. They can appear as well marginated or ill-defined nodules; and hazy changes in the surrounding fat or fascia may be present or not. Penetration of the fascial margins or invasion of deeper structures strongly suggest malignancy. Fig.: Subcutaneous metastasis from breast carcinoma. References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Page 12 of 33 Fig.: Soft tissue metastasis from renal cell carcinoma. References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Page 13 of 33 Fig.: Subcutaneous metastasis References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Melanoma Subcutaneous metastasis Subcutaneous metastases from primary melanoma are not uncommon in patients with Clark level IV or V lesions. These metastases may appear in unpredictable locations, on the basis of the site of the primary malignancy or of the patterns of lymphatic drainage. Metastatic melanoma may appear as multiple subcutaneous nodules. They may be the only radiologic manifestation of metastatic disease. Page 14 of 33 Fig.: Melanoma subcutaneous metastasis. References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Subcutaneous lymphatic tumor spread: Page 15 of 33 Fig.: Carcinomatous subcutaneous lymphangitis appears with an edema-like pattern with linear hyperdensities with a honeycomb appearance in the subcutaneous tissue References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Surgical tumor implantation: Fig.: 69-year-old man with a right malignant pleural mesothelioma who developed tumor implants along the chest tube up to the skin. Page 16 of 33 References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Inflammatory-infectious conditions Inflammatory-infectious conditions •Subcutaneous edema (although this entity is not exactly an inflammatory-infectious condition, it will be here considered because of the overlapping CT features with some of the inflammatory-infectious diseases). •Panniculitis •Cellulitis •Abscess •Skin fistula Subcutaneous edema Subcutaneous edema can appear related to many entities. CT scan usually demonstrates skin and subcutaneous tissue thickening, nonenhancing honeycomb appearance within the subcutaneous tissue with normal appearance of the subfascial compartment. Fig.: Subcutaneous edema References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Page 17 of 33 Panniculitis The panniculitis are a group of heterogeneous inflammatory diseases involving the subcutaneous fat. The specific diagnosis of the inflammatory disease that is involving the subcutis requires histopathologic study. CT features may be subtle or inapparent in many of these entities, but when visible, these include skin thickening, swelling of the affected area, increased attenuation of the subcutaneous tissue and occasional enhancement in the acute stage. Some panniculitis can evolve to fibrosis and scar formation. Some entities with evident imaging findings by MDCT have here been considered: -postirradiation panniculitis (Fig 1) -traumatic panniculitis (Fig 2, 3) Cellulitis Cellulitis is a bacterial infection of the cutaneous and subcutaneous tissues, without gross suppuration. CT findings are similar to those encountered in the panniculitis. Abscess Focal collection of pus with a rim of enhancement. It may contain gas. With time the abscess may become walled off and may be associated with diffuse inflammation. Page 18 of 33 Fig.: Subcutaneous abscess References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Skin fistulas CT findings of skin fistulas consist in dense tubular images extending from an infected collection to the skin, traversing the subcutis. Surrounding subcutaneous fat stranding may be present. Page 19 of 33 Fig.: Skin fistulas References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Foreign bodies and ST occupation Foreign bodies and subcutaneous tissue occupation •Calcifications •Subcutaneous emphysema •Hernias •Post-operative changes •Surgical and therapeutic devices •Foreign body injections Calcifications Calcifications in the subcutaneous tissue can appear in a variety of systemic diseases such as disorders of the calcium and phosphate metabolism or connective tissue Page 20 of 33 diseases as well as in localized damages (as in the case of injection granulomas or chronic calcified hematomas). Dermatomyositis is a rare, multisystem connective tissue disease, affecting the skin, subcutaneous tissue, and the fascia. Dystrophic calcification of unknown etiology, but possibly the result of damage from prior disease activity, develops in up to 40% of juvenile dermatomyositis patients and is a major contributor to morbidity. Fig.: Distrophic subcutaneous calcifications in a patient with dermatomyositis References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Injection granulomas from prior injections of parenteral drugs are common in the softtissues of the buttock and usually are calcified. Page 21 of 33 Fig.: Calcified injection granulomas in the buttocks (arrows) References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Subcutaneous emphysema Fig.: Subcutaneous emphysema Page 22 of 33 References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Hernias Internal tissues or organs may protrude through the thoracic cage or the abdominal wall into the subcutaneous tissue. Fig.: Abdominal and thoracic hernias References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Surgical and therapeutic devices such as sutures, stitches, prosthetic meshes, or portcatheters can be found in the subcutaneous tissue. Page 23 of 33 Fig.: Surgical and therapeutic devices References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Post-operative changes in the subcutaneous tissue as part of disease treatments are frequent. A wide variety of structures (colon segments, ureters, vascular grafts…) can lodge in the subcutaneous tissue. Page 24 of 33 Fig.: Post-operative changes References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Foreign body injections Foreign body injections into the subcutaneous tissue elicit a host response that attempts to remove the injected material. Inflammatory nodules may develop at the injection sites many years later, and are seen on CT as small nodules of soft-tissue attenuation. Fig.: Diffuse anterior thoracic wall panniculitis associated with nodules (siliconomas, red arrows) secondary to direct silicone injections in the breast References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Characterization of the subcutaneous nodules, frequently encountered by radiologists, starts with the evaluation of some imaging criteria such as homogeneity and density, border definition, presence and type of calcification, definition of adjacent fat (presence of hazy changes or air in the surrounding fat), vessel or nerve involvement and involvement of the fascia/muscular compartment. Infrequently, the CT appearance is so distinctive that a specific diagnosis can be suggested, as in the case of lipomas and vascular malformations. Page 25 of 33 Caution must be exercised when attempting to differentiate benign from malignant lesions solely on the basis of CT appearance, because of the overlap that exists between the imaging characteristics of both entities. Desmoid tumors are histologically benign fibrous neoplasms originating from the musculoaponeurotic structures throughout the body, but often appear as infiltrative and locally aggressive tumors. Abcesses and hemorrhage may have a CT appearance overlapping that of malignant neoplasms. The clinical history and physical examination will often provide key information to reach a single diagnosis or establish a suitably ordered differential diagnosis. Basic questions considering patient's presentation, history of previous lesions or underlying malignancy, history of previous surgery or radiation, previous trauma or use of anticoagulants, and evolution of lesion size and number, are essential. Multiple lesions should always alert the radiologist, particularly when examining cancer patients and above all, those with previous metastatic disease. Radiological criteria indicating metastasis: 1)The lesion and the primary tumor or the lesion and known metastasis elsewhere in the body change in size concurrently on serial CT examinations. 2) Newly appearing multiple lesions or enlargement of a lesion in a patient without a known metastatic focus elsewhere and a previous cancer history. Many times, follow-up examinations are key for reaching the correct diagnosis since millimetric lesions are not always sufficiently evident for consideration. Page 26 of 33 Fig.: Patient with a history of disseminated lung carcinoid tumor with hepatic metastasis. Is the subcutaneous tissue normal appearing? References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN Page 27 of 33 Fig.: The subcutaneous tissue already showed a metastatic focus in the right buttock in February 2008 (red arrow). This lesion was not recognized until March 2009, when CT was carried out on the basis of a positive PET examination at the level of the gluteus. References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN When a subcutaneous nodule cannot be characterized as a specific entity, further evaluation is required, starting with MR imaging. MR imaging is well-suited for the evaluation of soft tissue tumors and tumor-like lesions because of its intrinsically high soft-tissue contrast and capability for multiplanar image acquisition. However, characterization of soft tissue lesions is not always possible. When a lesion remains as indeterminate, biopsy should be considered to exclude malignancy. Early recognition of metastatic disease can lead to accurate and prompt diagnosis and timely treatment. Recognition of cutaneous and subcutaneous metastases often dramatically alters therapeutic plans, especially when metastases represent persistent cancer originally thought to be cured. Page 28 of 33 Images for this section: Fig. 1: Post-irradiation panniculitis: Radiation changes visible on CT scans are confined to the radiation therapy port and include skin thickening, ill-defined fat planes, streaks or linear changes in the subcutaneous tissues that cause a subtle increase in the attenuation of the fat, and changes in the adjacent internal organs. Fibrosis usually occurs within 30 months of treatment. Page 29 of 33 Fig. 2: Traumatic panniculitis secondary to subcutaneous injections of low-molecularweight heparin (LMWH): Traumatic panniculitis related to subcutaneous injections of LMWH are usually located in the subcutaneous fat of the anterior abdominal wall at or caudal to the level of the umbilicus, the typical injection site. They usually manifest as multiple subcutaneous nodular lesions, with poor defined borders and CT attenuation values similar to water. Hazy changes and/or air in the adjacent subcutaneous fat are frequent findings. Page 30 of 33 Fig. 3: Chronic evolution of traumatic panniculitis Page 31 of 33 Conclusion This exhibit should familiarize the audience with the normal subcutaneous tissue and the wide spectrum of pathologies that can be found in this region. Abnormalities in this region, although rare, may be the only sign of widespread malignancies. In oncologic patients, the imaging findings should be carefully correlated with the patient's clinical history and the growth trends of the primary tumor or metastatic deposits elsewhere. Personal Information References • • • • • • • • Requena L. Normal subcutaneous fat, necrosis of adipocytes and classification of the panniculitides. Semin Cutan Med Surg 2007; 26:66-70. Weekes RG, McLeod RA, Reiman HM, Pritchard DJ. CT of soft-tissue neoplasms. AJR 1985; 144:355-360. Beaman FD, Kransdorf MJ, Andrews TR, Murphey MD, Arcara LK, Keeling JH. Superficial soft-tissue masses: analysis, diagnosis, and differential considerations. Radiographics 2007; 27:509-523. 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