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PSOAS hypertrophy mimicking retroperitoneal tumor in a child with abdominal pain

      To the Editor:—Diagnosing a retroperitoneal lesion, especially psoas compartment disease, is sometimes difficult when using only conventional radiographs, and a comprehensive list of pathogenic entities must be considered. Although the advent of computed tomography (CT) has markedly improved our understanding of disease patterns and has proved useful in assessing both the location and extent of retroperitoneal injuries, it is expensive and not cost-beneficial in some circumstances. A unique kidney, ureter, and bladder (KUB) image of a pediatric patient, who presented at our pediatric ED with an acute abdomen, resulted in an initially misleading diagnosis that required confirmation from an abdominal CT scan. To the best of our knowledge, this is the first pediatric case discussed in the field of EM and radiology literature.
      A 15-year-old boy presented at our pediatric ED with a 5-day history of abdominal pain, nausea, and mild loose stool passage. The characteristic of his abdominal pain was dull, episodic cramps that subsided spontaneously. There was no associated vomiting, fever, dysuria, or loss of weight. Previous trauma insult or recent surgical interventions were denied. His medical history was otherwise unremarkable, except for thalassemia minor. On physical examination, this boy was well-developed and well-nourished, and, in general, healthy. There was mild tenderness without significant rebound pain over the periumbilical area. The bowel sounds were normal and the abdomen was without a palpable mass. The ED KUB had been arranged to rule out functional gastrointestinal problems such as stool impaction. However, it showed a suspected retroperitoneal mass incidentally with a remarkably bulging psoas margin (Fig 1). Abdominal sonography was performed in the ED, but no visible lesion was found in the abdominal cavity. Advanced studies, including a CT scan of the abdomen, were done. On the CT scan, there was no space-occupying lesion or any other pathologic mass found in the retroperitoneal area, but the psoas muscles were markedly hypertrophied (Fig 2) and symmetrically corresponded to the pseudotumor seen on the KUB. Neither pelvicalyceal system was dilated and no visible lesion was found in the peritoneal cavity. The laboratory data showed no evidence of leukocytosis or anemia except for a microcystic change (mean corpuscular volume: 67.3 μm3). Renal and liver functions were within the normal range and the inflammatory index level (C-reactive protein) was not elevated. The admission course was uneventful and the abdominal pain resolved after conservative treatment.
      Figure thumbnail GR1
      FIGURE 1Emergency room radiogram of the kidney, ureter, and bladder (KUB) showing suspected retroperitoneal mass with remarkably bulging psoas margin (arrowhead).
      Figure thumbnail GR2
      FIGURE 2(A) Intravenous contrast helical computed tomography scan at the upper lumbar level reveals normal thickness of psoas muscle. (B) The same computed tomography scan over the L3/L4 level demonstrates bulky hypertrophied psoas muscles without intra- or retroperitoneal lesions.
      The differential diagnosis between life-threatening diseases and benign lesions in the ED remains a challenge to both radiologists and EPs. The retroperitonium is relatively inaccessible to conventional roentgenologic imaging techniques. Many radiographic signs of retroperitoneal lesions depend on indirect evidence such as displacement of the ureter or alternation of the psoas margin.
      • Ralls P.W
      • Boswell W
      • Henderson R
      • et al.
      CT of inflammatory disease of the psoas muscle.
      The appearance of the psoas margin varies according to local pathologic conditions such as hematoma, abscess, and retroperitoneal tumors.
      • Feldberg M.A.M
      • Koehler P.R
      • Van Waes P.F.G.M
      Psoas compartment disease studied by computed tomography.
      ,
      • Stephens D.H
      • Sheedy P.F
      • Robert R.H
      • et al.
      Diagnosis and evaluation of retroperitoneal tumors by computed tomography.
      However, obliteration of the psoas shadow is not a reliable indicator of a pathogenic process; some benign variants could mimic acute abdominal conditions.
      • Zeiss J
      • Smith R.R
      • Taha A.M
      Iliopsoas hypertrophy mimicking acute abdomen in a bodybuilder.
      This patient’s tumor-like lesion was brought to our attention only because of a delineated shadow on his KUB radiograph. The massive psoas muscles were not large enough to indent the patient’s bowel or be accompanied by acute urinary retention,
      • Frank R.G
      Retroperitoneal mass and hydronephrosis.
      and some of the patient’s gastrointestinal problems could have been coincidental. The patient’s history was remarkable only for lifting dumbbells in a body-building program designed to build up his back and trunk muscles immediately before hospitalization.
      The psoas muscle is a major flexor of the hip. It stabilizes the lumbar spine while standing and walking, and it contributes to compressive and shear forces at the lumbar intervertebral discs during specific exercises. It reaches its maximum cross-sectional areas (CSAs) at the L4/L5 level. This is why patients with bowel displacement or hydroureter by a hypertrophic psoas is always at this level. Our patient demonstrates a similar clinical presentation, except for symmetric CSAs over the L3/L4 level, and is the youngest subject reported in the literature.
      Hypertrophy of the psoas muscles is a benign anatomic variant that could be recognized easily on a KUB image and might need an abdominal CT to confirm the normal entity. A CT scan is an effective screening modality because it provides not only an etiologic explanation of retroperitoneal lesion, but also because it directs appropriate clinical management. However, the cost and effectiveness of a CT scan for diagnosing an acute abdomen in a pediatric ED seems to be another challenging issue.
      • Garcia Pena B.M
      • Taylor G.A
      • Fishman S.J
      • et al.
      Costs and effectiveness of ultrasonography and limited computed tomography for diagnosing appendicitis in children.
      More evidence is needed to establish a clinical algorithm that allows ED physicians to avoid a costly and time-consuming workup for a benign condition. With physical fitness becoming a national trend, it is important to recognize the more common entity we described. A detailed history and a careful examination continue to play important roles in diagnosing this normal variant.

      References

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