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Outside the Inside: A Review of Soft-Tissue Abnormalities Seen on Thoracoabdominal Computed Tomography
Canadian Association of Radiologists Journal xx (2014) 1e8 www.carjonline.org
Computed Tomography / Tomodensitometrie
Outside the Inside: A Review of Soft-Tissue Abnormalities Seen on Thoracoabdominal Computed Tomography Susan J. Frank, MD, Shari Friedman, MD, Milana Flusberg, MD, Ellen L. Wolf, MD, Marjorie W. Stein, MD* Department of Radiology, Montefiore Medical Center, Bronx, New York, USA
Abstract In this review, we illustrate the computed tomographic features of thoracoabdominal soft-tissue abnormalities, which may be easily overlooked and often can provide important information regarding systemic processes. Examples include necrotizing fasciitis, heterotopic ossification, fat necrosis, benign and malignant neoplasms, endometriosis, and collagen vascular disease as well as systemic and congenital pathology. Resume Cette revue permet d’illustrer les caracteristiques tomodensitometriques des anomalies des tissus mous, lesquelles peuvent facilement passer inaperc¸ues et souvent s’averer une source de renseignements importants sur les processus systemiques. Elle porte notamment sur la fasciite necrosante, l’ossification heterotopique, la steatonecrose, les tumeurs benignes et malignes, l’endometriose, la collagenose avec manifestations vasculaires et les affections systemiques et congenitales. Ó 2014 Canadian Association of Radiologists. All rights reserved.
Computed tomography (CT) is routinely ordered for the evaluation of thoracic, abdominal, and pelvic pathology. Soft-tissue abnormalities, often incidental, are frequent and easily overlooked. It is important that the radiologist be familiar with the appearance and differential diagnosis of soft-tissue abnormalities on CT. This pictorial essay will review the CT features of common and uncommon softtissue infections; postoperative complications; benign and malignant neoplasms; endometriosis; and vascular, congenital, and systemic conditions. Infections Abdominal-wall infections include cellulitis, necrotizing fasciitis, and abscesses. Infections may be primary, postoperative, or posttraumatic, or associated with foreign bodies, or due to extension of intra-abdominal infection. CT findings in cellulitis include subcutaneous fat stranding and skin and fascial * Address for correspondence: Marjorie W. Stein, MD, Department of Radiology, Montefiore Medical Center, 111 East 210th Street, Bronx, New York 10467, USA. E-mail address: [email protected] (M. W. Stein).
thickening. Necrotizing fasciitis is life threatening and may be difficult to distinguish from cellulitis, particularly in its early stages. Subcutaneous gas is diagnostic in the appropriate clinical setting but is only reported in 55% of cases [1]. CT is useful in determining the extent of involvement, particularly when the infection involves the deep subcutaneous tissues (Figure 1) or intra-abdominal space. Fournier gangrene is a subtype of severe necrotizing fasciitis that involves the perineum, frequently seen in male patients with diabetes [2]. Pilonidal sinus disease results from chronic hair follicle infection with subcutaneous abscess formation and discharge through a midline draining sinus (Figure 2). Imaging is helpful to differentiate pilonidal sinus disease, which originates subcutaneously, from perianal fistulas, which communicate with the anus or the rectum [3]. CT is helpful in demonstrating these abscesses and fistulas. Postoperative Appearances There are normal and abnormal postoperative appearances of the subcutaneous tissues. Mild skin thickening, subcutaneous oedema, seromas, small hematomas, and gas within the soft tissues may be seen in the immediate postoperative period. Infection in this setting is suggested when fever or
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after surgery [4,5]. It is hypothesized to be due to either excessive suture line tension, metaplasia of mesenchymal embryonal cells, or intraoperative seeding of perichondrial cells [5]. CT reveals ossification within an incision, between the anterior abdominal fascia and the peritoneum (Figure 3) [5]. Heterotopic ossification can contain cartilage, bone, and fatty marrow [5e7]. The ability of CT to differentiate ossification from calcification, which is due to dystrophic deposits of calcium phosphate salts, is important because the treatment for heterotopic ossification is often surgical. CT also allows differentiation of heterotopic ossification from other palpable soft-tissue masses, including a retained foreign body, wound infection, and tumour seeding [5]. Fat Necrosis Subcutaneous fat necrosis may be due to trauma, collagen vascular disease, myeloproliferative disease, pancreatitis, pancreatic cancer, or, rarely, exposure to cold [8,9]. Fat necrosis, when due to trauma, may occur long after the inciting event. On CT, it typically appears as a well-defined subcutaneous fat-density mass with peripheral enhancement and calcification (Figure 4). Alternatively, it may be visualized as a globular soft-tissue density with central fat [8]. Soft-Tissue Neoplasms
Figure 1. (A) A 67-year-old woman after a ventral hernia repair with mesh (arrow). Axial noncontrast computed tomography (CT), demonstrating a large fluid collection with gas in the anterior abdominal wall typical of infection. (B) A 28-year-old man with sacral decubitus ulcer. Contrast-enhanced axial CT, demonstrating a large amount of gas within the gluteus muscles and subcutaneous inflammatory stranding typical for necrotizing fasciitis.
Soft-tissue tumours may be benign or malignant, primary or metastatic. Although magnetic resonance imaging is the modality of choice for soft-tissue tumour assessment, CT is also helpful in assessing matrix mineralization, bony involvement, and vascularity. Benign Neoplasms
leukocytosis is present. Postsurgical heterotopic ossification is a form of myositis ossificans traumatica and occurs only in subxiphoid, midline, vertical abdominal incisions. It is more common in men and has been reported as early as 11 days
Lipomas are very common benign soft-tissue tumours, frequently seen incidentally, more often in women, and are multiple in 5%. Typical locations include the back, shoulders, abdomen, and extremities. Lipomas are usually superficial but
Figure 2. A 42-year-old man with pilonidal sinus disease. Axial noncontrast computed tomography, demonstrating a sinus tract (arrow) that extends from the midline, which does not communicate with the rectum.
Figure 3. A 50-year-old woman after abdominal surgery. Contrast-enhanced computed tomography, demonstrating heterotopic ossification of the midline incision (arrow).
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Figure 4. A 62-year-old woman after abdominal surgery. Contrast-enhanced computed tomography, demonstrating foci of fat necrosis, with peripheral enhancement and calcification in the anterior abdominal wall.
Figure 6. A 31-year-old man with periscapular fatty mass (arrow) seen on contrast-enhanced computed tomography. The typical location and density favors a hibernoma.
may be intramuscular. On CT, lipomas measure fat density, often contain fibrous septations, and may contain calcifications or induce cortical thickening in adjacent bone (Figure 5). Septations are usually thin, smooth, and nonenhancing compared with their malignant counterparts, but imaging overlap exists with well-differentiated liposarcomas [7,10]. A hibernoma, a variant of a lipoma, is a benign tumour composed of brown fat, often located in the thigh or near the scapula. On CT, it exhibits fatty, or slightly higher, attenuation, and may demonstrate serpentine vasculature and mild capsular enhancement (Figure 6). Although fluorodeoxyglucose avid on positron emission tomographyeCT, it may be distinguished from malignancy by its characteristic location and CT attenuation [10]. Elastofibroma is a rare benign tumour composed of fibrous tissue and fat, most frequently found in elderly women. Sixty percent are bilateral and are characteristically located in the infrascapular region, deep to the serratus anterior and latissimus dorsi muscles. On CT, the mass is typically soft-tissue attenuation, with dense striations and fatty streaks (Figure 7) [11]. Neurofibromas may be plexiform, localized, or diffuse. They may be associated with neurofibromatosis when multiple
or plexiform. On CT, a neurofibroma appears as a fusiform soft-tissue mass in close proximity to a nerve and may erode bone (Figure 8). It is typically isodense to muscle on noncontrast CT, with a variable enhancement pattern after intravenous contrast [10]. Desmoid tumour is a deep fibromatosis, which is benign but notorious for local recurrence. It commonly occurs between 25 and 35 years of age, and may be seen with familial adenomatous polyposis. Although 70% occur in the extremities, women taking oral contraceptives or who are recently postpartum have an increased incidence of desmoids in the rectus abdominis and internal oblique muscles. On CT, desmoids are ill defined or spiculated, iso- or hyperdense, and enhance after intravenous contrast [12].
Figure 5. A 47-year-old man with intramuscular fatty mass (arrow) seen incidentally on this contrast-enhanced computed tomography.
Malignant Neoplasms Liposarcoma is seen in middle-aged and elderly patients, typically in the thigh, gluteal region, retroperitoneum, or lower extremity. Features of fatty lesions that increase suspicion for
Figure 7. A 78-year-old man with classically located infrascapular elastofibroma (arrow) seen on noncontrast computed tomography.
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Figure 8. A 27-year-old man with neurofibromatosis I and multiple intraabdominal and subcutaneous neurofibromas seen on contrast-enhanced computed tomography.
Figure 10. A 33-year-old man with AIDS and Kaposi sarcoma. Contrastenhanced computed tomography, demonstrating an avidly enhancing subcutaneous lesion in the right anterior chest wall. A lung mass is also present.
malignancy include large size, thick septa, nodular solid components, and contrast enhancement. Poorly differentiated liposarcomas may not have visualized fat [7,10]. Malignant fibrous histiocytoma, also referred to as pleomorphic undifferentiated sarcoma, occurs most often in the lower extremities, especially the thigh. It appears as a heterogeneously enhancing soft-tissue mass frequently causing adjacent bone destruction. The mass may occasionally contain bone, cartilage, fibrous tissue, hemorrhage, or necrosis [10]. Granulocytic sarcoma (chloroma) predominately occurs in a subcutaneous or intramuscular location, in patients younger than 15 years who have acute or chronic myelogenous leukaemia or other myeloproliferative disorders. Chloromas characteristically appear as slightly hypodense masses compared with muscle and with homogeneous contrast enhancement (Figure 9) [13]. Kaposi sarcoma, often an AIDS-defining illness, is linked to herpes virus type 8 infection. It most commonly presents as hyperenhancing subcutaneous nodules (Figure 10) [14].
Soft-tissue metastases are most often identified in the abdominal and chest wall, back, thigh, and shoulder (Figure 11). Lung cancer is the most common primary tumour to metastasize to soft tissues followed by kidney, colon, and melanoma. Softtissue metastases may be the first sign of malignancy [15].
Figure 9. A 53-year-old man with chronic myelogenous leukaemia. Axial contrast-enhanced computed tomography, demonstrating a hyperdense subcutaneous chloroma (arrow), an unusual appearance because most chloromas are hypodense to muscle.
Endometriosis Endometriosis is a common gynaecologic condition that occurs in 15% of menstruating women, almost exclusively in the pelvis. It may also form in a surgical scar after caesarean section, hysterotomy, hysterectomy, or laparotomy. The incidence of abdominal-wall endometriomas after a caesarean section varies from 0.03%e1% [16,17]. Endometrial deposits have been reported in the dermal and subcutaneous tissues, and, infrequently, in the rectus abdominis muscle and rectus sheath [18]. Scar endometriosis typically presents as a cyclically enlarging palpable abdominal-wall
Figure 11. A 35-year-old woman with metastatic cervical cancer. Contrastenhanced computed tomography, demonstrating multiple subcutaneous metastases.
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mass with increased tenderness during menses. CT typically reveals an enhancing solid mass in the abdominal wall, often with adjacent inflammatory stranding (Figure 12). The appearance varies, depending on the phase of the menstrual cycle, relative proportion of stroma, and the amount of hemorrhage and fibrosis. Magnetic resonance imaging may be useful to confirm the presence of blood products [16e18]. Medical management with progestational agents is often unsuccessful, and endometriomas may recur when hormonal treatment is terminated. Thus, surgery is the treatment of choice, and CT is useful in presurgical planning [16e18]. Sebaceous Cyst The term ‘‘sebaceous cyst’’ includes epidermal inclusion cysts that occur in relatively hairless parts of the body, and pilar cysts, which are associated with hair follicles. Sebaceous cysts contain keratin but do not contain sebum. They occur due to blocked sebaceous glands or hair follicles, or excessive testosterone production. Common locations include the scalp, face, neck, trunk, back, and scrotum. They exhibit variable CT attenuation, depending on their content, and are characteristically located in the subcutaneous tissues just beneath the skin surface. Steatocystoma multiplex is a rare autosomal dominant disorder of the pilosebaceous unit. Patients with steatocystoma multiplex present with numerous sebum and keratin-containing intradermal cysts, often on the chest (Figure 13) [10,19].
[20]. Pseudo-prune-belly syndrome is the term used when the syndrome occurs unilaterally or in female patients [21]. Treatment is directed towards relief of obstruction to prevent infection and kidney damage [20]. Cross-sectional imaging can also be useful to determine the practicality of cosmetic repair [21].
Eagle-Barret Syndrome
Acquired Muscle Atrophy
Eagle-Barret or prune belly syndrome occurs exclusively in male patients and is characterized by congenital absence or hypoplasia of the abdominal-wall muscles in association with genitourinary abnormalities (Figure 14). Cryptorchidism is always present. Varying degrees of urinary tract obstruction are seen, including urinary bladder enlargement
Acquired muscle atrophy of the abdominal-wall musculature may result from disuse or denervation. On CT, muscular atrophy is seen as fatty replacement of muscle (Figure 15). The atrophy is typically diffuse when secondary to muscular dystrophy, cerebral palsy, or quadriplegia, and is unilateral or asymmetric when due to cerebral vascular accident, poliomyelitis, trauma, or surgery [10].
Figure 12. A 26-year-old woman with history of caesarean section. Noncontrast computed tomography, demonstrating a pathologically proven endometrioma that appears as a soft-tissue nodule (arrow) in the midline abdominal wall caesarean section scar with adjacent stranding.
Figure 13. A 28-year-old woman with steatocystoma multiplex. Noncontrast computed tomography, demonstrating multiple fat and fluid density subcutaneous nodules.
Figure 14. A 4-year-old boy with Eagle-Barret syndrome. Axial noncontrast computed tomography, demonstrating characteristic absence of the abdominal-wall musculature and marked hydroureteronephrosis.
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Figure 17. A 61-year-old woman with end-stage renal disease. Contrastenhanced computed tomography, demonstrating metastatic calcification in the soft tissues of the pelvis, with multiple fluid-calcium levels (arrow).
pattern of calcification in the skin, subcutaneous tissues, and fascial planes termed calcinosis universalis [7]. Calcinosis circumscripta refers to dermal papules, plaques, and subcutaneous nodules seen in the early stages of polymyositis, dermatomyositis, lupus, and scleroderma, which may contain calcifications [22]. Interstitial lung disease may be visualized (Figure 16). Renal Disease
Figure 15. Muscle atrophy. (A) An 80-year-old man after a hip fracture with unilateral gluteal muscle atrophy (arrow) due to disuse seen on noncontrast computed tomography. (B) A 43-year-old man with muscular dystrophy with diffuse muscle atrophy.
Patients with chronic renal failure commonly develop periarticular calcium deposits. Metastatic calcification refers to the deposition of calcium in normal soft tissues secondary to elevated serum calcium from an abnormality of calcium metabolism [7]. These deposits can be mass-like with fluidcalcium levels that render them indistinguishable from idiopathic tumoural calcinosis (Figure 17) [22].
Collagen Vascular Disease
Vascular Pathology
Autoimmune connective tissue disorders such as polymyositis and dermatomyositis can demonstrate a sheet-like
Vascular lesions are typically low density, with areas of heterogeneity secondary to vascular, fibrous, and fatty
Figure 16. A 46-year-old woman with mixed connective tissue disorder. Axial noncontrast computed tomography, demonstrating subcutaneous calcifications (arrow) and honeycombing at the lung bases.
Figure 18. A 44-year-old man with right paraspinal hemangioma (arrow). Noncontrast computed tomography, demonstrating classic appearance with fat, vessels, and phleboliths.
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Rectus Sheath Hematoma Rectus sheath hematoma (RSH) often presents with sudden onset of abdominal pain and a palpable abdominal mass. RSH is more frequent in women and may occur after minimal trauma, such as coughing, or with exercise. RSH may be due to damaged inferior or superior epigastric arteries or tears of the muscle. Anticoagulation is a predisposing factor [23]. On CT, RSH appears as a lenticular-shaped mass when above the arcuate line and as a spherical mass when below the line. This difference in shape is due to the different anatomic composition of the posterior rectus sheath below the arcuate line. The density varies with the age of the hematoma, which is generally hyperdense acutely, may develop a hematocrit level, and becomes iso- or hypodense over time (Figure 20). Figure 19. A 59-year-old man with end-stage renal disease. Contrastenhanced computed tomography, demonstrating extensive collateral vessels in the abdominal wall due to multiple central venous stenoses from longstanding indwelling hemodialysis catheters.
tissue. Low-flow lesions, such as venous malformations, are visualized as soft-tissue masses with phleboliths and vessels that enhance after contrast. Arteriovenous fistulas or malformations are high-flow lesions that typically demonstrate large feeding arteries and draining veins. CT angiography can aid in preoperative planning by delineating the anatomy and venous drainage patterns [7]. Hemangioma is a common benign vascular neoplasm, frequently seen in children. On CT, it appears as a soft-tissue mass, often with calcified phleboliths and enhancing tortuous vessels (Figure 18). Cavernous intramuscular forms may have large fatty components. Patients with portal venous hypertension or central venous obstruction can demonstrate collateral veins in the chest and abdominal wall (Figure 19). This is often seen in association with subcutaneous oedema, characterized by stranding within the subcutaneous fat, more prominent in the dependent tissues [21].
Figure 20. An 84-year-old woman on anticoagulation. Noncontrast computed tomography, demonstrating moderate-sized left rectus sheath hematoma with hematocrit level.
Conclusions Soft-tissue abnormalities are common and easily overlooked on routine thoracoabdominal CT. Radiologists must carefully evaluate the soft tissues, which can reveal unsuspected abnormalities and provide information about systemic processes. Familiarity with CT features of soft-tissue lesions, including location, the relationship to adjacent structures, attenuation and enhancement patterns, can aid in establishing the correct diagnosis and in guiding optimal patient management. References [1] Wysoki MG, Santora TA, Shah RM, et al. Necrotizing fasciitis: CT characteristics. Radiology 1997;203:859e63. [2] Rajan DK, Scharer KA. Radiology of Fournier’s gangrene. AJR Am J Roentgenol 1998;170:163e8. [3] Taylor S, Halligan S, Bartram C. Pilonidal sinus disease: MR imaging distinction from fistula in ano. Radiology 2003;226:662e7. [4] Rosa M, Amir M. Myositis ossificans traumatica of the abdominal wall. Can J Surg 2009;52:e33e4. [5] Jacobs JE, Birnbaum BA, Siegelman ES. Heterotopic ossification of midline abdominal incisions: CT and MR imaging findings. AJR Am J Roentgenol 1996;166:579e84. [6] Balboni TA, Gobezie R, Mamon HJ. Heterotopic ossification: pathophysiology, clinical features, and the role of radiotherapy for prophylaxis. Int J Radiat Oncol Biol Phys 2006;65:1289e99. [7] Subhawong TY, Fishman EK, Swart JE, et al. Soft-tissue masses and masslike conditions: what does CT add to diagnosis and management? AJR Am J Roentgenol 2010;194:1559e67. [8] Chan LP, Gee R, Keogh C, et al. Imaging features of fat necrosis. AJR Am J Roentgenol 2003;181:955e9. [9] Lee SK, Lee JH, Han CH, et al. Calcified subcutaneous fat necrosis induced by prolonged exposure to cold weather: a case report. Pediatr Radiol 2001;31:294e5. [10] Resnick D, Kransdorf M. Bone and Joint Imaging. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2005. pp. 1199e243. [11] Ochsner JE, Sewall SA, Brooks GN, et al. Elastofibroma dorsi. RadioGraphics 2006;26:1873e6. [12] Robbin M, Murphey M, Temple HT, et al. Imaging of musculoskeletal fibromatosis. Radiographics 2001;21:585e600. [13] Guermazi A, Feger C, Rousselot, et al. Granulocytic sarcoma (chloroma) imaging findings in adults and children. AJR Am J Roentgenol 2002;178:319e25. [14] Restrepo C, Martinez S, Lemos J. Imaging manifestations of Kaposi’s sarcoma. Radiographics 2006;26:1169e85.
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[15] Plaza J, Perez-Montiel D, Mayerson J, et al. Metastases to soft tissues. Cancer 2008;112:193e203. [16] Hensen JJ, Vreisman ACV, Puylaert JBCM. Abdominal wall endometriosis: clinical presentation and imaging features with emphasis on sonography. AJR Am J Roentgenol 2006;186:616e20. [17] Dwivedi AJ, Agrawal SN, Silva YJ. Abdominal wall endometriomas. Dig Dis Sci 2002;47:456e61. [18] Kafkasli A, Franklin RR, Sauls D. Endometriosis in the uterine wall cesarean section scar. Gynecol Obstet Invest 1996;42:211e3. [19] Sonnenblick E, Buchness R, Austin J. CT demonstration of steatocystoma multiplex. J Comput Tomogr 1986;10:357e9.
[20] Eagle JR, Barret GS. Congenital deficiency of abdominal musculature with associated genitourinary abnormalities: a syndrome: report of nine cases. Pediatrics 1950;6:721e36. [21] Donnelly L, Frush D. Cross-sectional imaging of abnormalities of the abdominal wall in pediatric patients. AJR Am J Roentgenol 2001;176: 1233e9. [22] Olsen K, Chew F. Tumoral calcinosis: pearls, polemics, and alternative possibilities. Radiographics 2006;26:871e85. [23] Berna JD, Garcia-Medina V, Guirao J, et al. Rectus sheath hematoma: diagnostic classification by CT. Abdom Imaging 1996; 21:62e4.
Computed Tomography / Tomodensitometrie
Outside the Inside: A Review of Soft-Tissue Abnormalities Seen on Thoracoabdominal Computed Tomography Susan J. Frank, MD, Shari Friedman, MD, Milana Flusberg, MD, Ellen L. Wolf, MD, Marjorie W. Stein, MD* Department of Radiology, Montefiore Medical Center, Bronx, New York, USA
Abstract In this review, we illustrate the computed tomographic features of thoracoabdominal soft-tissue abnormalities, which may be easily overlooked and often can provide important information regarding systemic processes. Examples include necrotizing fasciitis, heterotopic ossification, fat necrosis, benign and malignant neoplasms, endometriosis, and collagen vascular disease as well as systemic and congenital pathology. Resume Cette revue permet d’illustrer les caracteristiques tomodensitometriques des anomalies des tissus mous, lesquelles peuvent facilement passer inaperc¸ues et souvent s’averer une source de renseignements importants sur les processus systemiques. Elle porte notamment sur la fasciite necrosante, l’ossification heterotopique, la steatonecrose, les tumeurs benignes et malignes, l’endometriose, la collagenose avec manifestations vasculaires et les affections systemiques et congenitales. Ó 2014 Canadian Association of Radiologists. All rights reserved.
Computed tomography (CT) is routinely ordered for the evaluation of thoracic, abdominal, and pelvic pathology. Soft-tissue abnormalities, often incidental, are frequent and easily overlooked. It is important that the radiologist be familiar with the appearance and differential diagnosis of soft-tissue abnormalities on CT. This pictorial essay will review the CT features of common and uncommon softtissue infections; postoperative complications; benign and malignant neoplasms; endometriosis; and vascular, congenital, and systemic conditions. Infections Abdominal-wall infections include cellulitis, necrotizing fasciitis, and abscesses. Infections may be primary, postoperative, or posttraumatic, or associated with foreign bodies, or due to extension of intra-abdominal infection. CT findings in cellulitis include subcutaneous fat stranding and skin and fascial * Address for correspondence: Marjorie W. Stein, MD, Department of Radiology, Montefiore Medical Center, 111 East 210th Street, Bronx, New York 10467, USA. E-mail address: [email protected] (M. W. Stein).
thickening. Necrotizing fasciitis is life threatening and may be difficult to distinguish from cellulitis, particularly in its early stages. Subcutaneous gas is diagnostic in the appropriate clinical setting but is only reported in 55% of cases [1]. CT is useful in determining the extent of involvement, particularly when the infection involves the deep subcutaneous tissues (Figure 1) or intra-abdominal space. Fournier gangrene is a subtype of severe necrotizing fasciitis that involves the perineum, frequently seen in male patients with diabetes [2]. Pilonidal sinus disease results from chronic hair follicle infection with subcutaneous abscess formation and discharge through a midline draining sinus (Figure 2). Imaging is helpful to differentiate pilonidal sinus disease, which originates subcutaneously, from perianal fistulas, which communicate with the anus or the rectum [3]. CT is helpful in demonstrating these abscesses and fistulas. Postoperative Appearances There are normal and abnormal postoperative appearances of the subcutaneous tissues. Mild skin thickening, subcutaneous oedema, seromas, small hematomas, and gas within the soft tissues may be seen in the immediate postoperative period. Infection in this setting is suggested when fever or
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after surgery [4,5]. It is hypothesized to be due to either excessive suture line tension, metaplasia of mesenchymal embryonal cells, or intraoperative seeding of perichondrial cells [5]. CT reveals ossification within an incision, between the anterior abdominal fascia and the peritoneum (Figure 3) [5]. Heterotopic ossification can contain cartilage, bone, and fatty marrow [5e7]. The ability of CT to differentiate ossification from calcification, which is due to dystrophic deposits of calcium phosphate salts, is important because the treatment for heterotopic ossification is often surgical. CT also allows differentiation of heterotopic ossification from other palpable soft-tissue masses, including a retained foreign body, wound infection, and tumour seeding [5]. Fat Necrosis Subcutaneous fat necrosis may be due to trauma, collagen vascular disease, myeloproliferative disease, pancreatitis, pancreatic cancer, or, rarely, exposure to cold [8,9]. Fat necrosis, when due to trauma, may occur long after the inciting event. On CT, it typically appears as a well-defined subcutaneous fat-density mass with peripheral enhancement and calcification (Figure 4). Alternatively, it may be visualized as a globular soft-tissue density with central fat [8]. Soft-Tissue Neoplasms
Figure 1. (A) A 67-year-old woman after a ventral hernia repair with mesh (arrow). Axial noncontrast computed tomography (CT), demonstrating a large fluid collection with gas in the anterior abdominal wall typical of infection. (B) A 28-year-old man with sacral decubitus ulcer. Contrast-enhanced axial CT, demonstrating a large amount of gas within the gluteus muscles and subcutaneous inflammatory stranding typical for necrotizing fasciitis.
Soft-tissue tumours may be benign or malignant, primary or metastatic. Although magnetic resonance imaging is the modality of choice for soft-tissue tumour assessment, CT is also helpful in assessing matrix mineralization, bony involvement, and vascularity. Benign Neoplasms
leukocytosis is present. Postsurgical heterotopic ossification is a form of myositis ossificans traumatica and occurs only in subxiphoid, midline, vertical abdominal incisions. It is more common in men and has been reported as early as 11 days
Lipomas are very common benign soft-tissue tumours, frequently seen incidentally, more often in women, and are multiple in 5%. Typical locations include the back, shoulders, abdomen, and extremities. Lipomas are usually superficial but
Figure 2. A 42-year-old man with pilonidal sinus disease. Axial noncontrast computed tomography, demonstrating a sinus tract (arrow) that extends from the midline, which does not communicate with the rectum.
Figure 3. A 50-year-old woman after abdominal surgery. Contrast-enhanced computed tomography, demonstrating heterotopic ossification of the midline incision (arrow).
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Figure 4. A 62-year-old woman after abdominal surgery. Contrast-enhanced computed tomography, demonstrating foci of fat necrosis, with peripheral enhancement and calcification in the anterior abdominal wall.
Figure 6. A 31-year-old man with periscapular fatty mass (arrow) seen on contrast-enhanced computed tomography. The typical location and density favors a hibernoma.
may be intramuscular. On CT, lipomas measure fat density, often contain fibrous septations, and may contain calcifications or induce cortical thickening in adjacent bone (Figure 5). Septations are usually thin, smooth, and nonenhancing compared with their malignant counterparts, but imaging overlap exists with well-differentiated liposarcomas [7,10]. A hibernoma, a variant of a lipoma, is a benign tumour composed of brown fat, often located in the thigh or near the scapula. On CT, it exhibits fatty, or slightly higher, attenuation, and may demonstrate serpentine vasculature and mild capsular enhancement (Figure 6). Although fluorodeoxyglucose avid on positron emission tomographyeCT, it may be distinguished from malignancy by its characteristic location and CT attenuation [10]. Elastofibroma is a rare benign tumour composed of fibrous tissue and fat, most frequently found in elderly women. Sixty percent are bilateral and are characteristically located in the infrascapular region, deep to the serratus anterior and latissimus dorsi muscles. On CT, the mass is typically soft-tissue attenuation, with dense striations and fatty streaks (Figure 7) [11]. Neurofibromas may be plexiform, localized, or diffuse. They may be associated with neurofibromatosis when multiple
or plexiform. On CT, a neurofibroma appears as a fusiform soft-tissue mass in close proximity to a nerve and may erode bone (Figure 8). It is typically isodense to muscle on noncontrast CT, with a variable enhancement pattern after intravenous contrast [10]. Desmoid tumour is a deep fibromatosis, which is benign but notorious for local recurrence. It commonly occurs between 25 and 35 years of age, and may be seen with familial adenomatous polyposis. Although 70% occur in the extremities, women taking oral contraceptives or who are recently postpartum have an increased incidence of desmoids in the rectus abdominis and internal oblique muscles. On CT, desmoids are ill defined or spiculated, iso- or hyperdense, and enhance after intravenous contrast [12].
Figure 5. A 47-year-old man with intramuscular fatty mass (arrow) seen incidentally on this contrast-enhanced computed tomography.
Malignant Neoplasms Liposarcoma is seen in middle-aged and elderly patients, typically in the thigh, gluteal region, retroperitoneum, or lower extremity. Features of fatty lesions that increase suspicion for
Figure 7. A 78-year-old man with classically located infrascapular elastofibroma (arrow) seen on noncontrast computed tomography.
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Figure 8. A 27-year-old man with neurofibromatosis I and multiple intraabdominal and subcutaneous neurofibromas seen on contrast-enhanced computed tomography.
Figure 10. A 33-year-old man with AIDS and Kaposi sarcoma. Contrastenhanced computed tomography, demonstrating an avidly enhancing subcutaneous lesion in the right anterior chest wall. A lung mass is also present.
malignancy include large size, thick septa, nodular solid components, and contrast enhancement. Poorly differentiated liposarcomas may not have visualized fat [7,10]. Malignant fibrous histiocytoma, also referred to as pleomorphic undifferentiated sarcoma, occurs most often in the lower extremities, especially the thigh. It appears as a heterogeneously enhancing soft-tissue mass frequently causing adjacent bone destruction. The mass may occasionally contain bone, cartilage, fibrous tissue, hemorrhage, or necrosis [10]. Granulocytic sarcoma (chloroma) predominately occurs in a subcutaneous or intramuscular location, in patients younger than 15 years who have acute or chronic myelogenous leukaemia or other myeloproliferative disorders. Chloromas characteristically appear as slightly hypodense masses compared with muscle and with homogeneous contrast enhancement (Figure 9) [13]. Kaposi sarcoma, often an AIDS-defining illness, is linked to herpes virus type 8 infection. It most commonly presents as hyperenhancing subcutaneous nodules (Figure 10) [14].
Soft-tissue metastases are most often identified in the abdominal and chest wall, back, thigh, and shoulder (Figure 11). Lung cancer is the most common primary tumour to metastasize to soft tissues followed by kidney, colon, and melanoma. Softtissue metastases may be the first sign of malignancy [15].
Figure 9. A 53-year-old man with chronic myelogenous leukaemia. Axial contrast-enhanced computed tomography, demonstrating a hyperdense subcutaneous chloroma (arrow), an unusual appearance because most chloromas are hypodense to muscle.
Endometriosis Endometriosis is a common gynaecologic condition that occurs in 15% of menstruating women, almost exclusively in the pelvis. It may also form in a surgical scar after caesarean section, hysterotomy, hysterectomy, or laparotomy. The incidence of abdominal-wall endometriomas after a caesarean section varies from 0.03%e1% [16,17]. Endometrial deposits have been reported in the dermal and subcutaneous tissues, and, infrequently, in the rectus abdominis muscle and rectus sheath [18]. Scar endometriosis typically presents as a cyclically enlarging palpable abdominal-wall
Figure 11. A 35-year-old woman with metastatic cervical cancer. Contrastenhanced computed tomography, demonstrating multiple subcutaneous metastases.
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mass with increased tenderness during menses. CT typically reveals an enhancing solid mass in the abdominal wall, often with adjacent inflammatory stranding (Figure 12). The appearance varies, depending on the phase of the menstrual cycle, relative proportion of stroma, and the amount of hemorrhage and fibrosis. Magnetic resonance imaging may be useful to confirm the presence of blood products [16e18]. Medical management with progestational agents is often unsuccessful, and endometriomas may recur when hormonal treatment is terminated. Thus, surgery is the treatment of choice, and CT is useful in presurgical planning [16e18]. Sebaceous Cyst The term ‘‘sebaceous cyst’’ includes epidermal inclusion cysts that occur in relatively hairless parts of the body, and pilar cysts, which are associated with hair follicles. Sebaceous cysts contain keratin but do not contain sebum. They occur due to blocked sebaceous glands or hair follicles, or excessive testosterone production. Common locations include the scalp, face, neck, trunk, back, and scrotum. They exhibit variable CT attenuation, depending on their content, and are characteristically located in the subcutaneous tissues just beneath the skin surface. Steatocystoma multiplex is a rare autosomal dominant disorder of the pilosebaceous unit. Patients with steatocystoma multiplex present with numerous sebum and keratin-containing intradermal cysts, often on the chest (Figure 13) [10,19].
[20]. Pseudo-prune-belly syndrome is the term used when the syndrome occurs unilaterally or in female patients [21]. Treatment is directed towards relief of obstruction to prevent infection and kidney damage [20]. Cross-sectional imaging can also be useful to determine the practicality of cosmetic repair [21].
Eagle-Barret Syndrome
Acquired Muscle Atrophy
Eagle-Barret or prune belly syndrome occurs exclusively in male patients and is characterized by congenital absence or hypoplasia of the abdominal-wall muscles in association with genitourinary abnormalities (Figure 14). Cryptorchidism is always present. Varying degrees of urinary tract obstruction are seen, including urinary bladder enlargement
Acquired muscle atrophy of the abdominal-wall musculature may result from disuse or denervation. On CT, muscular atrophy is seen as fatty replacement of muscle (Figure 15). The atrophy is typically diffuse when secondary to muscular dystrophy, cerebral palsy, or quadriplegia, and is unilateral or asymmetric when due to cerebral vascular accident, poliomyelitis, trauma, or surgery [10].
Figure 12. A 26-year-old woman with history of caesarean section. Noncontrast computed tomography, demonstrating a pathologically proven endometrioma that appears as a soft-tissue nodule (arrow) in the midline abdominal wall caesarean section scar with adjacent stranding.
Figure 13. A 28-year-old woman with steatocystoma multiplex. Noncontrast computed tomography, demonstrating multiple fat and fluid density subcutaneous nodules.
Figure 14. A 4-year-old boy with Eagle-Barret syndrome. Axial noncontrast computed tomography, demonstrating characteristic absence of the abdominal-wall musculature and marked hydroureteronephrosis.
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Figure 17. A 61-year-old woman with end-stage renal disease. Contrastenhanced computed tomography, demonstrating metastatic calcification in the soft tissues of the pelvis, with multiple fluid-calcium levels (arrow).
pattern of calcification in the skin, subcutaneous tissues, and fascial planes termed calcinosis universalis [7]. Calcinosis circumscripta refers to dermal papules, plaques, and subcutaneous nodules seen in the early stages of polymyositis, dermatomyositis, lupus, and scleroderma, which may contain calcifications [22]. Interstitial lung disease may be visualized (Figure 16). Renal Disease
Figure 15. Muscle atrophy. (A) An 80-year-old man after a hip fracture with unilateral gluteal muscle atrophy (arrow) due to disuse seen on noncontrast computed tomography. (B) A 43-year-old man with muscular dystrophy with diffuse muscle atrophy.
Patients with chronic renal failure commonly develop periarticular calcium deposits. Metastatic calcification refers to the deposition of calcium in normal soft tissues secondary to elevated serum calcium from an abnormality of calcium metabolism [7]. These deposits can be mass-like with fluidcalcium levels that render them indistinguishable from idiopathic tumoural calcinosis (Figure 17) [22].
Collagen Vascular Disease
Vascular Pathology
Autoimmune connective tissue disorders such as polymyositis and dermatomyositis can demonstrate a sheet-like
Vascular lesions are typically low density, with areas of heterogeneity secondary to vascular, fibrous, and fatty
Figure 16. A 46-year-old woman with mixed connective tissue disorder. Axial noncontrast computed tomography, demonstrating subcutaneous calcifications (arrow) and honeycombing at the lung bases.
Figure 18. A 44-year-old man with right paraspinal hemangioma (arrow). Noncontrast computed tomography, demonstrating classic appearance with fat, vessels, and phleboliths.
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Rectus Sheath Hematoma Rectus sheath hematoma (RSH) often presents with sudden onset of abdominal pain and a palpable abdominal mass. RSH is more frequent in women and may occur after minimal trauma, such as coughing, or with exercise. RSH may be due to damaged inferior or superior epigastric arteries or tears of the muscle. Anticoagulation is a predisposing factor [23]. On CT, RSH appears as a lenticular-shaped mass when above the arcuate line and as a spherical mass when below the line. This difference in shape is due to the different anatomic composition of the posterior rectus sheath below the arcuate line. The density varies with the age of the hematoma, which is generally hyperdense acutely, may develop a hematocrit level, and becomes iso- or hypodense over time (Figure 20). Figure 19. A 59-year-old man with end-stage renal disease. Contrastenhanced computed tomography, demonstrating extensive collateral vessels in the abdominal wall due to multiple central venous stenoses from longstanding indwelling hemodialysis catheters.
tissue. Low-flow lesions, such as venous malformations, are visualized as soft-tissue masses with phleboliths and vessels that enhance after contrast. Arteriovenous fistulas or malformations are high-flow lesions that typically demonstrate large feeding arteries and draining veins. CT angiography can aid in preoperative planning by delineating the anatomy and venous drainage patterns [7]. Hemangioma is a common benign vascular neoplasm, frequently seen in children. On CT, it appears as a soft-tissue mass, often with calcified phleboliths and enhancing tortuous vessels (Figure 18). Cavernous intramuscular forms may have large fatty components. Patients with portal venous hypertension or central venous obstruction can demonstrate collateral veins in the chest and abdominal wall (Figure 19). This is often seen in association with subcutaneous oedema, characterized by stranding within the subcutaneous fat, more prominent in the dependent tissues [21].
Figure 20. An 84-year-old woman on anticoagulation. Noncontrast computed tomography, demonstrating moderate-sized left rectus sheath hematoma with hematocrit level.
Conclusions Soft-tissue abnormalities are common and easily overlooked on routine thoracoabdominal CT. Radiologists must carefully evaluate the soft tissues, which can reveal unsuspected abnormalities and provide information about systemic processes. Familiarity with CT features of soft-tissue lesions, including location, the relationship to adjacent structures, attenuation and enhancement patterns, can aid in establishing the correct diagnosis and in guiding optimal patient management. References [1] Wysoki MG, Santora TA, Shah RM, et al. Necrotizing fasciitis: CT characteristics. Radiology 1997;203:859e63. [2] Rajan DK, Scharer KA. Radiology of Fournier’s gangrene. AJR Am J Roentgenol 1998;170:163e8. [3] Taylor S, Halligan S, Bartram C. Pilonidal sinus disease: MR imaging distinction from fistula in ano. Radiology 2003;226:662e7. [4] Rosa M, Amir M. Myositis ossificans traumatica of the abdominal wall. Can J Surg 2009;52:e33e4. [5] Jacobs JE, Birnbaum BA, Siegelman ES. Heterotopic ossification of midline abdominal incisions: CT and MR imaging findings. AJR Am J Roentgenol 1996;166:579e84. [6] Balboni TA, Gobezie R, Mamon HJ. Heterotopic ossification: pathophysiology, clinical features, and the role of radiotherapy for prophylaxis. Int J Radiat Oncol Biol Phys 2006;65:1289e99. [7] Subhawong TY, Fishman EK, Swart JE, et al. Soft-tissue masses and masslike conditions: what does CT add to diagnosis and management? AJR Am J Roentgenol 2010;194:1559e67. [8] Chan LP, Gee R, Keogh C, et al. Imaging features of fat necrosis. AJR Am J Roentgenol 2003;181:955e9. [9] Lee SK, Lee JH, Han CH, et al. Calcified subcutaneous fat necrosis induced by prolonged exposure to cold weather: a case report. Pediatr Radiol 2001;31:294e5. [10] Resnick D, Kransdorf M. Bone and Joint Imaging. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2005. pp. 1199e243. [11] Ochsner JE, Sewall SA, Brooks GN, et al. Elastofibroma dorsi. RadioGraphics 2006;26:1873e6. [12] Robbin M, Murphey M, Temple HT, et al. Imaging of musculoskeletal fibromatosis. Radiographics 2001;21:585e600. [13] Guermazi A, Feger C, Rousselot, et al. Granulocytic sarcoma (chloroma) imaging findings in adults and children. AJR Am J Roentgenol 2002;178:319e25. [14] Restrepo C, Martinez S, Lemos J. Imaging manifestations of Kaposi’s sarcoma. Radiographics 2006;26:1169e85.
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[20] Eagle JR, Barret GS. Congenital deficiency of abdominal musculature with associated genitourinary abnormalities: a syndrome: report of nine cases. Pediatrics 1950;6:721e36. [21] Donnelly L, Frush D. Cross-sectional imaging of abnormalities of the abdominal wall in pediatric patients. AJR Am J Roentgenol 2001;176: 1233e9. [22] Olsen K, Chew F. Tumoral calcinosis: pearls, polemics, and alternative possibilities. Radiographics 2006;26:871e85. [23] Berna JD, Garcia-Medina V, Guirao J, et al. Rectus sheath hematoma: diagnostic classification by CT. Abdom Imaging 1996; 21:62e4.