Download Looking to the subcutaneous tissue

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.
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Varona , O. Persiva , J. Cáceres ; Barcelona/ES, Málaga/ES
Keywords:
Subcutaneous tissue, Multidetector computed tomography,
Thoracoabdominal wall
DOI:
10.1594/ecr2010/C-2357
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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
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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.
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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.
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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.
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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%).
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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
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Fig.: Soft tissue metastasis from renal cell carcinoma.
References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN
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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.
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Fig.: Melanoma subcutaneous metastasis.
References: J. Andreu; Radiology, Vall d'Hebron Hospital, Barcelona, SPAIN
Subcutaneous lymphatic tumor spread:
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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
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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
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