This copy is for personal use only. To order printed copies, contact [email protected] 88 Internal Hernias in the Era of Multidetector CT: Correlation of Imaging and Surgical Findings1 Satoshi Doishita, MD Tohru Takeshita, MD, PhD Clinical diagnosis of internal hernias is challenging because of their Yasutake Uchima, MD, PhD nonspecific signs and symptoms. Many types of internal hernias Masayasu Kawasaki, MD, PhD have been defined: paraduodenal, small bowel mesentery–related, Taro Shimono, MD, PhD greater omentum–related, lesser sac, transverse mesocolon–related, GASTROINTESTINAL IMAGING Akiyoshi Yamashita, MD pericecal, sigmoid mesocolon–related, falciform ligament, pelvic Michiko Sugimoto, MD internal, and Roux-en-Y anastomosis–related. An internal hernia is Teruhisa Ninoi, MD, PhD a surgical emergency that can develop into intestinal strangulation Hideki Shima, MD, PhD and ischemia. Accurate preoperative diagnosis is crucial for appro- Yukio Miki, MD, PhD priate management. Multidetector computed tomography (CT), with its thin-section axial images, high-quality multiplanar reforma- Abbreviations: MPR = multiplanar reforma- tions, and three-dimensional images, currently plays an essential tion, 3D = three-dimensional role in preoperative diagnosis of internal hernias. The diagnostic RadioGraphics 2016; 36:88–106 approach to internal hernias at multidetector CT includes detecting Published online 10.1148/rg.2016150113 an intestinal closed loop, identifying the hernia orifice, and analyz- Content Codes: ing abnormal displacement of surrounding structures and key ves- 1From the Department of Diagnostic and In- sels around the hernia orifice and hernia sac. At each step, multide- terventional Radiology, Osaka City University tector CT can depict pathognomonic findings. A saclike appearance Graduate School of Medicine, 1-4-3, Asahi- suggests an intestinal closed loop in several types of internal herni- machi, Abeno-ku, Osaka 545-8585, Japan (S.D., T.T., T.S., Y.M.); Department of Surgery, Fu- as. Convergence, engorgement, and twisting of mesenteric vessels in chu Hospital, Izumi, Japan (Y.U.); Department the hernia orifice can be seen clearly at multidetector CT, especially of Surgery, Bell Land General Hospital, Sakai, Japan (M.K.); Department of Radiology, Japa- with use of multiplanar reformations. For definitive diagnosis of an nese Red Cross Medical Center, Tokyo, Japan internal hernia, analysis of displacement of anatomic landmarks (A.Y.); Department of Radiology, Japan Com- around the hernia orifice is particularly important, and thin-section munity Healthcare Organization (JCHO) Osaka Hospital, Osaka, Japan (M.S.); Department images provide the required information. Detailed knowledge of of Radiology, Perfect Liberty Hospital, Tonda- the anatomy, etiology, and imaging landmarks of the various hernia bayashi, Japan (T.N.); and Department of Radi- ology, Narita Red-Cross Hospital, Narita, Japan types is also necessary. Familiarity with the appearances of internal (H.S.). Presented as an education exhibit at the hernias at multidetector CT allows accurate and specific preopera- 2014 RSNA Annual Meeting. Received April 14, 2015; revision requested June 2 and received tive diagnosis. July 10; accepted July 31. For this journal-based © SA-CME activity, the authors, editor, and re- RSNA, 2015 • radiographics.rsna.org viewers have disclosed no relevant relationships. Address correspondence to S.D. (e-mail: sd@ med.osaka-cu.ac.jp). ©RSNA, 2015 Introduction Meyers et al (1) have defined an internal hernia as a protrusion of SA-CME LEARNING OBJECTIVES abdominal viscera through an opening within the confines of the After completing this journal-based SA-CME peritoneal cavity, although not all internal hernias are strictly intra- activity, participants will be able to: peritoneal. Orifices of internal hernias can be congenital or acquired. ■ Describe the diagnostic approach to Congenital orifices include a normal foramen or unusual peritoneal internal hernias with use of multidetec- fossae or recesses related to failure of peritoneal fusion, whereas tor CT. acquired orifices result from trauma, inflammation, or previous ■ Identify key vessels in the various types of surgery. In most cases, the herniated viscera are small bowel loops. internal hernias seen at multidetector CT. Internal hernia is classically reported to cause approximately 4% of ■ Discuss the imaging features of various types of internal hernias. cases of acute small bowel obstruction (2). See www.rsna.org/education/search/RG. Clinical signs and symptoms of internal hernia are nonspecific and overlap with those of other pathologic conditions in the abdomen. The most common clinical symptoms are nausea, vomiting, abdomi- nal pain, and abdominal distention (3). Patients present with a wide spectrum of symptoms, ranging from no symptoms to symptoms of acute small bowel obstruction. Internal hernias occasionally show RG • Volume 36 Number 1 Doishita et al 89 transmesenteric, and transomental. However, TEACHING POINTS this classification is neither fully systematic nor ■ Today, multidetector CT is the first-line imaging technique comprehensive. A modified classification and no- for internal hernia. Thin-section axial images and high-quality menclature is shown in Figure 1. Usually, hernia multiplanar reformations (MPRs) allow improved visualization of normal anatomic structures and pathologic conditions, types are named according to the location of the leading to greater diagnostic accuracy. Furthermore, three-di- hernia orifice. The exceptions are lesser sac, pel- mensional (3D) images such as volume-rendered images aid vic internal, and Roux-en-Y anastomosis–related in the understanding of pathologic conditions and contribute hernias, which can involve various hernia orifices. to optimal surgical planning. Internal hernias are divided into three cat- ■ Internal hernias are divided into three categories on the basis egories on the basis of the type of hernia orifice of the type of hernia orifice: (a) normal foramen, (b) unusual peritoneal fossa or recess into the retroperitoneum, and (c) (Table 1): (a) normal foramen, (b) unusual peri- abnormal opening in a mesentery or peritoneal ligament. toneal fossa or recess into the retroperitoneum, ■ Most mesenteries and peritoneal ligaments consist of two and (c) abnormal opening in a mesentery or peri- peritoneal layers. Abnormal openings can arise in only one toneal ligament. This categorization is important peritoneal layer or through both layers. Internal hernias associ- for a systematic radiologic approach to diagnosis. ated with an abnormal opening in a mesentery or peritoneal Most mesenteries and peritoneal ligaments ligament are subcategorized according to the degree of the consist of two peritoneal layers. Abnormal open- defect: (a) transmesenteric or fenestra type, if both peritoneal layers are involved; or (b) intramesenteric or pouch type, if ings can arise in only one peritoneal layer or either peritoneal layer is involved. through both layers. Internal hernias associated ■ A saclike appearance strongly supports a diagnosis of internal with an abnormal opening in a mesentery or peri- hernia. Unfortunately, this sign is not observed in all types of toneal ligament are subcategorized according to internal hernias. A saclike appearance can be observed with the degree of the defect (Fig 2): (a) transmesen- internal hernias into an unusual fossa in the retroperitoneum teric or fenestra type, if both peritoneal layers are or with intramesenteric-type internal hernias. involved; or (b) intramesenteric or pouch type, if ■ Definitive diagnosis of internal hernias requires identification either peritoneal layer is involved. of abnormal displacement of surrounding structures and key vessels around the hernia orifice and hernia sac. Detailed Classically, paraduodenal hernia has been knowledge of landmarks in the various types of internal her- reported as the most common type of internal nias is the key to diagnosis. hernia (1). However, reports of postoperative internal hernias, particularly after Roux-en-Y anastomosis reconstruction, have been increasing recently (6,9). Transmesenteric hernia is cur- spontaneous reduction, resulting in intermittent rently the most prevalent type, even if Roux-en- symptoms. For these reasons, precise clinical diag- Y anastomosis–related hernia is excluded (15). nosis of internal hernias is difficult. Current incidences of the various hernia types Multidetector computed tomography (CT) are thus difficult to ascertain. has established its status as a powerful diagnostic tool for acute abdomen, and this remains true for Multidetector CT Technique internal hernias. Although an increasing number Internal hernia is a challenging disorder for of pathognomonic CT findings of internal hernia clinicians to diagnose because of the nonspecific have been reported, the majority of such reports signs and symptoms. Clinical use of CT enables are individual case reports. Small numbers of inspection of the inside of the abdomen and review articles (4–8) and scientific studies (9–13) facilitates use of advanced diagnostic procedures have been published. (16). However, definitive diagnosis remained dif- This article provides an overview of the diag- ficult in the era before multidetector CT. nostic approach to internal hernias with use of Today, multidetector CT is the first-line imag- multidetector CT, with emphasis on tracing key ing technique for internal hernias. Thin-section vessels. In addition, various