Cross-Sectional Imaging of Abnormalities of the Abdominal Wall in Pediatric Patients

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1 Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved ross-sectional Imaging of bnormalities of the bdominal Wall in Pediatric Patients ross-sectional imaging with T or MR imaging has been shown to be helpful in depicting pathologic processes involving the abdominal wall [1 3]. Primarily, T and MR imaging may be performed to evaluate palpable lesions of the abdominal wall [2]. In addition, accurate identification of abnormalities of the anterior abdominal wall may provide important diagnostic clues when imaging studies are performed in a patient during an examination for intraabdominal disease. We review the cross-sectional imaging features of pathologic processes of the abdominal wall that we have encountered in our practice of pediatric body imaging. Processes reviewed are Pictorial Essay Lane F. Donnelly 1 and Donald P. Frush 2 grouped by causality congenital, inflammatory, traumatic, neoplastic, and vascular. ongenital Lesions ongenital abnormalities of the anterior abdominal wall include omphalocele, gastroschisis, and bladder extrophy. These severe abnormalities are obvious during the physical examination of a Fig. 1. ongenital anomalies of abdominal wall are revealed on T scans., Omphalocele in 8-day-old male neonate who underwent T to be evaluated for abscess after surgery. T scan shows liver (L) protruding through defect (arrows) in anterior abdominal wall., Infected urachal remnant in 4-year-old girl who underwent T to determine cause of abdominal pain and fever. T scan shows heterogeneous mass (arrows) in midline anterior to bladder. Note peripheral enhancement and central low attenuation within mass. Received ugust 23, 2000; accepted after revision September 20, Department of Radiology, hildren s Hospital Medical enter, 3333 urnet ve., incinnati, OH ddress correspondence to L. F. Donnelly. 2 Department of Radiology, Duke University Medical enter, Durham, N JR 2001;176: X/01/ merican Roentgen Ray Society JR:176, May

2 Donnelly and Frush Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved patient and are surgically repaired. Postnatal cross-sectional imaging does not play a primary role in the examination of these patients. However, these abnormalities may be encountered when T is performed to check for a potential intraabdominal process after surgery (Fig. 1). Fig. 2. Unilateral abdominal wall hypoplasia (pseudo prune-belly syndrome) in 2-week-old girl., oronal T1-weighted MR image (TR/TE, 500/11) shows outpouching (arrows) of abdominal wall in region of hypoplasia of abdominal musculature. Vertebral anomalies are also visible., xial T1-weighted MR image (500/11) shows hypoplasia (arrows) of abdominal musculature and subcutaneous fat. Note normal thickness of right abdominal muscles and subcutaneous fat. One congenital lesion that may initially be detected on cross-sectional imaging is a urachal abnormality. The urachus is an embryologic canal that connects the apex of the bladder and the umbilicus. Normally, this canal closes by the time of birth. If any portion Fig. 4. T scan shows extension of inflammation into abdominal wall from rohn s disease and abscess in 15-yearold girl. Marked thickening of descending colon (arrowhead) with surrounding phlegmon and abscess are revealed. Note asymmetric thickening of left external abdominal oblique, internal abdominal oblique, and transversus abdominis muscles (arrow) compared with those on right. Fig. 3. T scans reveal manifestations of wound infections., Wound abscess in 14-year-old boy 12 days after surgery for ruptured appendix. T scan shows focal area of low attenuation (arrow) within subcutaneous fat at surgical incision. Enhancing rim and gas within lesion are consistent with abscess. lso note several intraabdominal inflammatory fluid collections (arrowheads)., ellulitis without discrete abscess revealed in 14- year-old girl experiencing pain and fever 10 days after surgical removal of ovarian cyst. T scan shows poorly defined soft-tissue attenuation (arrows) within subcutaneous fat surrounding previous midline incision. No drainable fluid collection is seen. of this embryologic structure remains patent, a urachal abnormality results. The portion of the urachus that remains patent determines the type of the urachal anomaly present. If the urachus remains patent only at its mid portion and is closed both at its umbilical and bladder ends, a urachal cyst is formed. Patients with urachal cysts may present with a palpable mass, abdominal pain, tenderness, and fever, or with symptoms of a urinary tract infection. When T is performed to determine the cause of the patient s abdominal pain, a cystic mass anterosuperior to the bladder dome is revealed at the midline (Fig. 1). MR imaging has been recommended as an aid in planning surgery for infants with positive findings for prune-belly syndrome at examinations of their abdominal walls [4]. Prune-belly syndrome, or Eagle-arrett syn JR:176, May 2001

3 Imaging bdominal Wall bnormalities in Pediatric Patients Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved drome, is the name given to the triad of hypoplasia of the abdominal muscles, cryptorchidism, and abnormalities of the urinary tract system. The syndrome can be incomplete (pseudo prune-belly syndrome) occurring unilaterally or in girls. Determining the extent of abdominal wall hypoplasia and contents of the eventration with MR imaging has been advocated as being helpful in ascertaining the practicality of cosmetic repair, particularly in patients with the incomplete syndrome [4] (Fig. 2). Inflammatory Processes Inflammation of the subcutaneous tissue and muscle of the abdominal wall most commonly occurs after surgery or penetrating trauma [5]. In children, the wound infection is most commonly encountered after surgery for a ruptured appendix (Fig. 3). Wound infection may appear as a phlegmon, showing poorly defined areas of soft-tissue attenuation within the subcutaneous fat and poorly defined muscular borders, or the infection may appear as a discrete abscess, showing a well-defined fluid collection often with enhancing margins [6] (Fig. 3). Inflammation may also extend into the abdominal wall from extension of intraabdominal disease. In children, there may be abdominal inflammation caused by perforative appendicitis, typhlitis, rohn s disease (Fig. 4), or pancreatitis. In patients with pancreatitis, T may reveal abdominal wall involvement as an extension of inflammation and hemorrhage into the periumbilical area (Grey-Turner s sign at physical examination) (Fig. 5), as an extension of inflammation into Fig. 5. T scans reveal abdominal wall manifestations of pancreatitis., T scan shows Grey Turner s sign in 15-year-old boy with pancreatitis with extension of inflammation into transverse mesocolon and thickening of colonic wall (arrows). Soft-tissue stranding in subcutaneous fat of overlying abdominal wall (arrowheads) is consistent with extension of inflammation., T scan obtained at level just above umbilicus in same patient as in reveals extension of inflammation (arrow) to periumbilical area., T scan shows presumed subcutaneous fat necrosis in 16-year-old boy with pancreatitis. Multiple areas of soft-tissue attenuation (arrows) within subcutaneous fat of anterior and posterior abdominal wall. Fig. 6. T scan reveals abdominal wall calcifications formed after inflammation from colitis (presumed typhlitis) in 6-year-old boy. Marked thickening and calcifications involving right rectus abdominis, external abdominal oblique, internal abdominal oblique, and transversus abdominis muscles are identified by arrows. Residual thickening of hepatic flexure and transverse colon (arrowheads) is present from previous episode of colitis. the flanks (ullen s sign at physical examination), or as areas of subcutaneous fat necrosis (Fig. 5). We have also seen dystrophic muscular calcification occurring in the abdominal wall of children after episodes of extensive abdominal wall inflammation (Fig. 6). Primary infection of the abdominal wall is rare. However, necrotizing myofascitis can occur, particularly in children with compromised immune systems. It is a rapidly progressive soft-tissue infection characterized by widespread necrosis. MR imaging is the modality of choice for the evaluation of the extent of inflammation. When the infection involves the abdominal wall, the patient may present with symptoms mimicking those of an acute abdomen, and T may be performed [6]. T shows soft-tissue density within muscle planes (Fig. 7), Fig. 7. T scan depicts necrotizing myofascitis in 15- year-old immunocompromised boy who presented with acute abdominal pain and tenderness. Fluid attenuation (arrows) surrounding left rectus abdominis, external abdominal oblique, internal abdominal oblique, and transversus abdominis muscles is visible. Note replacement of surrounding subcutaneous fat with soft-tissue attenuation and similar but less prominent inflammation on right side. low attenuation and swelling of muscles, and, at times, soft-tissue gas. Without aggressive treatment, the disease can result in death. Traumatic bnormalities Traumatic injury can result in a number of abdominal wall abnormalities that can be detected on T, including laceration (Fig. 8), hematoma, and contusion [1, 3]. bdominal wall trauma may be seen on imaging when T is performed for evaluation of intraabdominal injury after blunt trauma, distribution of injury in penetrating trauma (Fig. 8), or other abdominal symptoms in patients for whom the history of trauma is occult (abuse or spontaneous hematoma). One of the more common causes of abdominal wall trauma in children is lap belt injury. In addition to in- JR:176, May

4 Donnelly and Frush Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved Fig. 8. T scans reveal manifestations of abdominal wall trauma., Degloving injury of abdominal wall in 12-year-old boy after trauma from lap belt. T scan shows absence of portion of subcutaneous tissues that extends to level of abdominal musculature (arrow). Underlying structures appear to be uninvolved., Penetrating injury from gunshot in 14-year-old boy. T scan reveals subcutaneous gas, abnormal soft-tissue density replacing subcutaneous fat, and metal density fragments within subcutaneous tissues of left abdominal wall (arrows). There was no evidence of involvement of peritoneal cavity., Transection of abdominal musculature in 10-year-old boy after lap belt injury. T scan shows marked thickening and indistinctness (arrows) of right rectus abdominis, external abdominal oblique, internal abdominal oblique, and transversus abdominis muscles compared with musculature on left. Muscles are discontinuous from anterior to posterior with gap containing herniated fat (arrowheads). Note large surrounding hematoma. D, T scan more inferior in same patient as in reveals areas of high attenuation (arrows) consistent with active arterial extravasation into region of hematoma. Fig. 9. Rectus hematoma in 15-yearold girl. T scan obtained to diagnose cause of abdominal pain shows enlargement and heterogeneous attenuation of right rectus muscle (arrows). traabdominal manifestations such as bowel injury, lap belt injuries can cause contusion or hematoma of the anterior abdominal wall or transection of the musculature [7] (Fig. 8). Rectus sheath hematoma may occur spontaneously or after minor trauma, and its manifestations may be occultly present, with the patient reporting abdominal pain and tenderness [3]. The diagnosis may not be considered clinically, and the lesion may be first identified when the patient undergoes T (Fig. 9). Traumatic injury may also be iatrogenic (Fig. 10). auses of abdominal wall abnormalities after surgery include hematoma, edema, or hernia [5] (Fig. 10). D 1236 JR:176, May 2001

5 Imaging bdominal Wall bnormalities in Pediatric Patients Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved Fig. 10. T scans reveal iatrogenic causes of abdominal wall abnormalities, nterior abdominal pain in 12-yearold girl undergoing peritoneal dialysis was caused by leaking dialysis fluid. T scan shows poorly defined soft-tissue attenuation (arrows) in subcutaneous fat in right anterior abdominal wall. Note dialysis catheter (arrowhead)., Postsurgical hernia in 8-year-old boy with remote history of splenectomy. T scan shows lateral hernia (arrows) containing bowel. Fig. 11. MR images reveal vascular malformations causing focal abdominal wall masses in children., xial gadolinium-enhanced fat-saturated T1-weighted MR image (TR/TE, 600/11) shows hemangioma presenting as palpable mass in 3-month-old female infant. Plaquelike mass (arrow) showing diffuse enhancement is confined to subcutaneous tissues., xial T1-weighted MR image (666/12) shows lymphatic malformation involving abdominal wall of 1-year-old boy. Multiloculated mass involves subcutaneous tissues of right posterior abdominal wall. Note overlying skin thickening (arrows). Lesion is confined to subcutaneous tissues. T2-weighted image (not shown) revealed mass (arrows) to be diffusely high in signal intensity. Fig. 12. T scan and MR image of other causes of benign abdominal wall lesions., T scan of 5-year-old girl with lipoma shows asymmetric thickening of subcutaneous fat (L) consistent with lipoma., xial T2-weighted MR image (TR/ TE, 5000/90) shows multiple high-signal-intensity masses (arrows) multiple neurofibromas within abdominal wall in 16-year-old girl with neurofibromatosis. Note paraspinal masses (arrowheads). Neoplastic and Vascular Masses number of benign and malignant masses can involve the abdominal wall. We typically use MR imaging to examine a patient with a palpable mass. One of the most common benign masses to involve the abdominal wall in children is a hemangioma or vascular malformation. Hemangiomas are the most common soft-tissue mass seen in children. MR imaging of proliferating hemangiomas (Fig. 11) typically shows a discrete lobulated mass that is hyperintense on T2-weighted MR images and typically enhances diffusely with the administration of gadolinium [8]. There may be large draining veins. Other vascular malformations that involve the abdominal wall are typically lowflow vascular malformations, such as venous or lymphatic malformations. The appearance of a low-flow vascular malformation on MR images depends on the composition of lymphatic and venous components [8] (Fig. 11). Other benign masses encountered in children include lipomas and neurofibromas (Fig. 12). With type I neurofibromatosis, numerous neurofibromas may be present in the abdominal wall of patients (Fig. 12). JR:176, May

6 Donnelly and Frush Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved In children, malignant lesions of the abdominal wall may be primary soft-tissue malignancies such as rhabdomyosarcoma (Fig. 13) or may represent metastatic disease. The most common cause of metastasis to the soft tissues in children is neuroblastoma (Fig. 13). Fig. 13. MR images and T scan of malignant abdominal wall lesions., xial T1-weighted MR image (TR/TE, 600/11) shows well-defined round mass (arrow) within subcutaneous fat posterior to right iliac wing in 15-year-old girl with undifferentiated sarcoma. Mass is slightly higher in signal intensity than adjacent muscle., xial T2-weighted fat-saturated MR image (2000/80) of same patient as in shows mass (arrow) to be heterogeneously high in signal intensity., xial T2-weighted MR image (2000/80) obtained with fat saturation shows multiple high-signal-intensity masses (arrows) involving right lateral abdominal wall adjacent to large adrenal mass (M) in 2-year-old girl with neuroblastoma involving abdominal wall. D, T scan shows unsuspected soft-tissue density mass (arrow) within subcutaneous tissues of posterior abdominal wall in 16-year-old boy with metastatic rhabdomyosarcoma to abdominal wall. Other Vascular-Related bnormalities Other abnormalities that may be found within the abdominal wall during imaging include those of vascular etiology. In cases of inferior vena cava obstruction or portal hypertension, collateral veins may be seen within the abdominal wall (Fig. 14). The identification of the vessels may aid in differentiating a thrombosed inferior vena cava from a nonopacified, nonobstructed inferior vena cava on contrast-enhanced T scans. The abdominal wall may also show signs of anasarca, or D Fig. 14. T scans of abdominal wall abnormalities with vascular causes., T scan shows venous collaterals within abdominal wall of 8-year-old girl with thrombosis of inferior vena cava. Multiple enhancing venous collaterals (arrows) within subcutaneous tissues of abdominal wall are visible. lot is identified in inferior vena cava (arrowhead)., T scan reveals marked subcutaneous edema in 5-year-old girl with Henoch-Schönlein purpura. Soft-tissue attenuation consistent with fluid adjacent to abdominal wall musculature can be seen in reticular pattern throughout subcutaneous tissues. Edema is most prominent in dependent posterior positions (arrows) JR:176, May 2001

7 Imaging bdominal Wall bnormalities in Pediatric Patients Downloaded from by on 02/06/18 from IP address opyright RRS. For personal use only; all rights reserved Fig. 15. T scan obtained to evaluate renal calculi in 14-year-old girl with muscular atrophy and history of myelomeningocele shows marked atrophy of the abdominal wall and paraspinal musculature. Note spinal dysraphism (arrow). edema, from any of a number of vascular causes (Fig. 14). This edema will appear as replacement of the subcutaneous fat with soft-tissue attenuation, often more prominent in the posterior, dependent portions of the abdominal wall. Diffuse muscular atrophy caused by neurologic deficits may also be evident on cross-sectional imaging (Fig. 15). In summary, a number of abnormalities can occur in the abdominal wall of children. ccurate identification of abnormalities of the anterior abdominal wall is important when imaging is performed to evaluate either abdominal wall or intraabdominal lesions. References 1. Stamm ER, Pretorius DH, Olson LK. bdominal wall T: a pictorial essay. omput Radiol 1985;9: Pandolfo I, landino, Gaeta M, Racchiusa S, hirico G. T findings in palpable lesions of the anterior abdominal wall. J omput ssist Tomogr 1986;10: Goodman P, Raval. T of the abdominal wall. JR 1990;154: Donnelly LF, Johnson JF III. Unilateral abdominal wall hypoplasia: radiographic findings in two infant girls. Pediatr Radiol 1995;25: Donnelly LF, Frush DP, O Hara SM, isset GS III. Necrotizing myofasciitis: an atypical cause of acute abdomen in an immunocompromised child. Pediatr Radiol 1998;28: Ghahremani GG, Gore RM. T diagnosis of postoperative abdominal complications. Radiol lin North m 1989;27: Hayes W, onway WF, Walsh JW, oppage L, Gervin S. Seat belt injuries: radiologic findings and clinical correlation. RadioGraphics 1991;11: Meyer JS, Hoffer F, arnes PD, Mulliken J. iological classification of soft-tissue vascular anomalies: MR correlation. JR 1991;157: JR:176, May