Small Bowel Anatomy & Obstruction PDF

S S · The duodenum has 4 parts: superior (D1), descending (D2), horizontal/transverse (D3) and ascending (D4). · Valvulae conniventes (also known as plicae circulares) are the circumferential small bowel folds....

S S · The duodenum has 4 parts: superior (D1), descending (D2), horizontal/transverse (D3) and ascending (D4). · Valvulae conniventes (also known as plicae circulares) are the circumferential small bowel folds. In contrast, colonic haustra are not circumferential. · The superior mesenteric artery (SMA) supplies both the jejunum and ileum while the duodenum receives blood from branches of the celiac axis. · A common small bowel mesentery anchors the jejunum and ileum to the posterior abdominal wall. · The jejunum features larger, closer together folds and larger villi compared to the ileum. · The Ligament of Treitz (suspensory muscle of the duodenum) is a thin muscle located at the junction of duodenum and the jejunum and serves as the divider between the upper and lower GI tract. This becomes clinically relevant when trying to localize the source of GI bleeding. It is not directly visualized by imaging, but can be indirectly located at the distant edge of the ascending (fourth) portion of the duodenum. An upper GI bleed is defined as occurring proximal to the Ligament of Treitz. A lower GI bleed occurs distally to the Ligament of Treitz. S SBO · Small bowel obstruction (SBO) is common and most often due to adhesions from prior surgery or hernia. Neoplasm, stricture, and intussusception are less common causes. Radiographic evaluation of small bowel obstruction · An abdominal radiograph is often the initial imaging evaluation for suspected obstruction. · Radiographic findings of SBO include small bowel distention >3 cm. Multiple air-fluid levels at different heights may be seen on the upright view. In addition, the lack of gas in the colon is especially suggestive of obstruction. · Differential diagnosis of dilated loops of small bowel on plain radiographs include: Post-operative adynamic ileus (recent history of surgery, will often see gas in the colon). Focal ileus related to inflammatory process (pancreatitis, enteritis, bowel dilatation may be focal near the location of inflammation). Ileus due to ascites: Ascites often compresses the ascending and descending colon and rectum as these structures are not on a mesentery. However, gas in the transverse colon and sigmoid colon is still apparent. Small bowel may be medialized. · A potential pitfall may be in a patient with a total colectomy or a bowel diversion where no gas will be seen in the colon and the small bowel caliber may be greater than normal by necessity. GI: 197 CT imaging of small bowel obstruction · CT is highly sensitive and specific for diagnosis of SBO. Small bowel distention ≥3 cm with a focal/discrete transition point to collapsed bowel is highly specific for a SBO. · Benefits of CT include confirmation of diagnosis of SBO, visualization of the etiology and assessment of complications of obstruction such as ischemia or strangulation. · It is important to approach the interpretation of an obstruction in a systematic way. · First, look for the transition point to decompressed bowel to determine the cause. · Second, always determine if the obstruction is simple or closed-loop (see below). A closed- loop obstruction is a never miss diagnosis as there is very high risk for bowel ischemia and therefore, severe morbidity and mortality. · Third, evaluate for signs of ischemia or impending ischemia, which include (in rough order of severity): Engorged mesenteric vessels. Mesenteric edema. Ascites surrounding the bowel or inter-loop uid, due to increased capillary permeability. Wall thickening, due to submucosal edema. Lack o bowel wall enhancement, due to vasoconstriction or underperfusion. Note that the presence or absence of bowel wall enhancement can only be assessed if positive oral contrast was not given. Pneumatosis intestinalis, which is gas in the bowel wall due to necrosis. Pneumatosis produces multiple small locules of gas seen circumferentially in the bowel wall. · In addition to small bowel distention >3 cm and a transition point to decompressed bowel, an additional helpful CT finding of SBO is the small bowel feces sign, which describes particulate feculent material mixed with gas bubbles in the small bowel that resembles the CT appearance of stool. The small bowel feces sign is often seen just proximal to the transition point and is helpful to localize the site of transition. The sign may be especially helpful in subacute or partial obstruction, which can otherwise be Small bowel feces sign: Axial CT shows an obstruction. A difficult to diagnose. loop of small bowel in the right lower quadrant (arrow) The sign is thought to be due to bacterial demonstrates numerous gas locules and particulate overgrowth and undigested food. material in the small bowel. GI: 198 Closed-loop obstruction Closed-loop obstruction in two different patients: Note the similar C-shape configuration of dilated small bowel loops with associated swirling of the mesentery, mesenteric edema, and inter-loop fluid (yellow arrow). There is segmental bowel wall hypoenhancement (red arrows) when compared to adjacent normally enhancing bowel loops, concerning for ischemia. · Closed-loop obstruction is a surgical emergency that may lead to bowel ischemia. Closed- loop obstruction represents obstruction of both the efferent and afferent segments of a single loop of bowel. Closed-loop obstruction is almost always seen in association with small bowel volvulus, which may be due to adhesions or internal hernia. · CT imaging features include the whirl sign due to twisting of mesenteric vessels seen in volvulus. Other CT findings include a U- or C-shaped distribution of the distended bowel loops with radially oriented vessels. Mesenteric edema is often present. Obstruction due to adhesions Small bowel obstruction due to adhesions: Coronal (left image) and sagittal CT (right image) shows multiple dilated, fluid-filled loops of small bowel. A transition point is located in the midline pelvis (arrows on sagittal image), with no obstructing mass or evidence of hernia. · Adhesions from prior surgery or intra-peritoneal inflammatory process are the most common cause of SBO. The vast majority of patients with SBO due to adhesions have had prior abdominal surgery. GI: 199 Obstruction due to adhesions (continued) · Adhesions are an imaging diagnosis of exclusion as they are not directly visualized by imaging. On CT, a transition point is seen, but no alternative cause for the transition (e.g., no mass or hernia, etc.) is identified. · In the absence of signs of impending ischemia, this is usually managed non-operatively with nasogastric tube decompression and bowel rest. Obstruction due to external hernia · Protrusion of bowel through an abdominal wall defect is the second most common cause of SBO. Approximately 75% of external hernias occur in the groin, with the majority being inguinal hernias. · The term strangulation refers to ischemia due to vascular compromise by the hernia. · The term incarceration refers to a hernia that cannot be reduced and is a physical exam finding, not an imaging finding. · An inguinal hernia may be either indirect or direct, depending on the relation of the hernia to the inferior epigastric vessels. Indirect: Indirect inguinal hernia is the most common type and is more common in males. The neck of the hernia is lateral to the inferior epigastric vessels. Hernia contents travel with the spermatic cord, often into the scrotum. Indirect inguinal hernias are considered congenital due to a patent processus vaginalis. Direct: The neck of a direct inguinal hernia is medial to the inferior epigastric vessels, protruding through a weak area in the anterior abdominal wall (Hesselbach’s triangle). The hernia contents do not go into the scrotum. These are considered acquired and may be caused by increased intra-abdominal pressure, such as obesity, COPD and chronic constipation. When an inguinal hernia contains the appendix, it is called an Amyand hernia. When it contains a Meckel’s diverticulum, it is called a Littre hernia. Direct inguinal hernia: Axial contrast-enhanced CT shows a direct inguinal hernia on the right containing a portion of the urinary bladder (yellow arrow). Note the right inferior epigastric vessels and inguinal canal contents (red arrow) are displaced laterally and compressed by the hernia. The right common femoral artery and vein are normal in caliber (blue arrows). GI: 200 Obstruction due to external hernia (continued) · In an obturator hernia, bowel herniates through the obturator canal. Obturator hernias are almost always seen in elderly women due to pelvic floor laxity. The key imaging finding is bowel located between the pectineus and obturator muscles. It is important to correctly diagnose an obturator hernia preoperatively. An obturator hernia requires a different surgery from inguinal hernia and has an especially high morbidity and mortality if incarcerated. Obturator hernia: Axial (left image) and coronal (right image) contrast-enhanced CT demonstrates herniation of a bowel loop (arrows) through the left obturator canal, between the obturator and pectineus muscles, with a resultant upstream SBO. · Ventral hernia is often due to prior laparotomy or other abdominal surgery. · Femoral hernia is a protrusion into the femoral canal posterior and inferior to the inguinal ligament. When it contains the appendix, it is called De Garengeot hernia. In addition to location below the inguinal ligament, it can be differentiated from an inguinal hernia by its tendency to compress the adjacent femoral vein. Femoral hernia: Axial (left image) and coronal (right image) contrast-enhanced CT shows herniation of a short segment of small bowel into the right femoral canal (yellow arrows), causing upstream SBO. Note the right femoral vein (red arrow) is compressed by the hernia. · Spigelian hernia is a lateral ventral hernia that occurs at the semilunar line (between the rectus abdominis and lateral oblique muscles). It is associated with ipsilateral cryptorchidism amongst male infants due to failure of development of a gubernaculum. · Richter hernia can occur in any of the above hernias and occurs when only the antimesenteric portion of the bowel wall is herniated. These hernias are more likely to result in strangulation than obstruction. GI: 201 Obstruction due to internal hernia · Protrusion of bowel through a defect or opening in the peritoneal cavity or mesentery is a relatively uncommon cause of SBO. Internal hernias carry a high rate of volvulus. If volvulus is present, the whirl sign may be visible. · Many different subtypes may be seen including transmesenteric, paraduodenal, and foramen of Winslow among others. · Transmesenteric hernia is a broad category of bowel herniation through defects in any of the three true mesenteries (small bowel mesentery, transverse mesocolon, and sigmoid mesentery). The most common type of transmesenteric hernia is the transmesocolic hernia due to a defect in the transverse mesocolon (mesentery of the transverse colon). Transmesocolic hernia is seen most commonly post Roux-en-Y gastric bypass or biliary- enteric anastomosis from liver transplant. · Paraduodenal hernia was previously the most common internal hernia (prior to the rise in gastric bypass surgery). Paraduodenal hernias are congenital anomalies, due to embryologic failure of mesenteric fusion and resultant mesenteric defect. They more commonly occur on the left and are associated with abnormal intestinal rotation. portal vein Fossa of Landzert SMV IMV SMA left colic artery IMA Fossa of Waldeyer Illustration demonstrating the anatomy most relevant to paraduodenal hernia. Note the fossa of Landzert (le paraduodenal hernia) and fossa of Waldeyer (right paraduodenal hernia). In the more common le paraduodenal hernia, the bowel can herniate through a mesenteric defect named fossa of Landzert, located to the left of the ascending (fourth portion) duodenum, behind the IMV. The key imaging finding is a cluster of small bowel loops between the pancreas and stomach. In a right paraduodenal hernia, the bowel and mesentery containing iliocolic, right colic, middle colic arteries herniate through the fossa of Waldeyer, a mesenteric defect located behind the SMA and SMV. GI: 202 Obstruction due to internal hernia (continued) · Foramen o Winslow hernia: The foramen of Winslow is the communication between the lesser sac and the greater peritoneal cavity. The key imaging features of a foramen of Winslow hernia are dilated loops of bowel in the lesser sac and presence of mesentery and/ or bowel loops between the IVC and main portal vein. Foramen of Winslow hernia: Axial (left image) and coronal (right image) T2-weighted MRI shows unusual configuration of the right hemicolon (yellow arrows), which extends into the lesser sac through the foramen of Winslow, displacing the stomach laterally (red arrows). There is no evidence of colonic wall thickening or pericolonic edema. Obstruction due to neoplasm · A mass intrinsic to the bowel or compression from an extrinsic mass may cause SBO. An extrinsic mass is usually straightforward to diagnose by CT. · Although the presence of an intraluminal mass may be more difficult to detect on CT, clues to the presence of an intrinsic mass include irregular bowel wall thickening and/or regional lymphadenopathy. · Primary small bowel neoplasm causing intrinsic bowel obstruction may be due to adenocarcinoma, GIST, and carcinoid. Metastatic causes of intrinsic bowel neoplasm include melanoma, ovarian, and lung cancer. Melanoma is known to cause intussusception. · Lymphoma is generally a “soft ” tumor and rarely causes obstruction. Aneurysmal dilatation of the small bowel wall is a classic appearance, but presentation is highly variable. Obstruction due to intussusception Intussusception causing small bowel obstruction: Coronal contrast-enhanced CT demonstrates a segmental jejunojejunal intussusception (arrows), causing an early or partial proximal small bowel obstruction. This was a case of metastatic melanoma (metastatic lesion not visualized on this image). · While transient intussusceptions are a common incidental finding, an intussusception causing obstruction should raise suspicion for an underlying lesion and prompt surgery. · Transient small bowel intussusceptions tend to be short segments without wall thickening or upstream obstruction, while malignant intussusceptions involve longer segments with associated wall thickening and upstream obstruction. GI: 203 Obstruction due to Crohn's disease Obstruction due to Crohn's ileitis: Coronal (left image) and axial contrast-enhanced CT shows dilated loops of proximal small bowel. The terminal ileum (yellow arrows) and several loops of distal ileum (red arrows) are thickened, reflecting enteritis. · Stricturing disease or active inflammation resulting in luminal narrowing is an important cause of bowel obstruction in Crohn’s disease. Crohn’s disease is discussed below. Obstruction due to gallstone · Gallstone ileus, which is actually misnomer, is a subtype of SBO due to a gallstone, which has eroded from gallbladder into the duodenum, causing the classic Rigler’s triad of pneumobilia (from cholecystoduodenal fistula), SBO, and ectopic gallstone within the small bowel. · Bouveret syndrome is a proximal form of gallstone ileus due to impaction of the gallstone in the pylorus or proximal duodenum. Bouveret syndrome and subsequent gallstone ileus: Top left image: Axial contrast-enhanced CT shows a cholecystoduodenal fistula (yellow arrows) and gastric distention. Top right image: Oral contrast only CT demonstrates contrast filling the cholecystoduodenal fistula (yellow arrow) and a mass-like structure in the duodenum outlined by surrounding contrast (red arrow), thought to represent a noncalcified gallstone. Bottom left image: Coronal contrast-enhanced CT obtained several days later shows new SBO with a subtle noncalcified gallstone in the terminal ileum (red arrow) at the transition point and the cholecystoduodenal fistula (yellow arrow). GI: 204 E · Enteritis is inflammation of the small bowel. The most common CT manifestation of enteritis is bowel wall thickening. Mesenteric stranding or free fluid may also be present. Crohn's disease · Crohn's disease is a chronic granulomatous inflammatory condition which may affect any part of the GI tract from the mouth to the anus, though most commonly involves the terminal ileum. Bowel involvement is discontinuous, with characteristic skip lesions with intervening normal GI tract. · The earliest histologic changes occur in the submucosa, seen on imaging as aphthous ulcers due to lymphoid hyperplasia and lymphedema. · There are three phenotypes that may exist independently or may coexist. Imaging findings include: Active in ammation: Mural hyperenhancement, intramural edema, mural ulcerations. Stricturing disease: Luminal narrowing with upstream dilatation. Penetrating disease : Sinus tracts, simple fistulas, complex fistulas, inflammatory mass, abscess. *Perianal disease is not considered penetrating disease. · Endoscopy and barium fluoroscopy (small bowel follow-through, enteroclysis, and barium enema) have historically been the modalities to evaluate Crohn's disease. CT and MR enterography are now the exams of choice. The advantages of CT and MRI are the ability to evaluate the entire bowel wall (not just the mucosa), presence of extraintestinal complications, and the vasculature. The disadvantages of CT and MRI compared to fluoroscopy and endoscopy are reduced spatial resolution and limited sensitivity for detecting subtle early signs of disease. · The most common imaging findings on all modalities are wall thickening and inflammatory changes of the terminal ileum. · Fluoroscopic findings include thickened, nodular folds in the affected regions of small bowel, luminal narrowing, mucosal ulceration, and separation of bowel loops (due to fibrofatty proliferation). The typical cobblestone appearance seen on endoscopy and fluoroscopy is a result of crisscrossing deep ulcerations. · CT/MRI findings of Crohn's disease include: Creeping fat describes widely separated loops of bowel due to fibrofatty proliferation. Comb sign describes engorged vasa recta (mesenteric blood vessels) adjacent to an inflamed bowel loop. Pseudosacculation describes the bulging appearance along the antimesenteric border which is spared compared to the fibrotic and shortened mesenteric side. Restricted diffusion, when seen with other findings of active inflammation, indicates more severe disease. · There is an increased risk of developing adenocarcinoma so close attention should be paid for any nodular thickening of the bowel wall. GI: 205 Crohn's disease (continued) Crohn's disease (terminal ileitis): Small bowel follow-through (left image) shows terminal ileum nodular fold thickening, mucosal ulceration, and separation of the terminal ileum (arrows) from adjacent loops of small bowel. Right lower quadrant color Doppler ultrasound (right image) in the same patient demonstrates the nodular fold thickening (arrows) and hyperemic wall. Case courtesy Michael Callahan, MD, Boston Children’s Hospital. Crohn's disease with stricturing disease: Small bowel follow-through (left image) shows the string sign (yellow arrows) representing segmental stricture in a loop of distal ileum, with a few small antimesenteric pseudosacculations (red arrows). Contrast-enhanced CT (right image) shows bowel wall thickening and fibrofatty mesenteric changes (blue arrows), known by pathologists and surgeons as creeping fat. Case courtesy Michael Callahan, MD, Boston Children’s Hospital. GI: 206 Crohn's disease (continued) Perirectal abscess and enterocutaneous fistula secondary to Crohn's disease: Contrast-enhanced CT (left image) shows a peripherally enhancing fluid collection to the right of the rectum (yellow arrows). T2-weighted MRI (right image) shows the distal portion of an enterocutaneous fistula extending to the skin surface (red arrow). There is marked subcutaneous edema (blue arrows) extending into the subcutaneous tissues of the right buttock. Case courtesy Michael Callahan, MD, Boston Children’s Hospital. Celiac disease (sprue, gluten-sensitive enteropathy) · Celiac disease, also known as sprue and gluten-sensitive enteropathy, is an autoimmune, proximal enteritis caused by a T-cell-mediated immune response triggered by antigens in ingested gluten. · The primary sites of involvement are the duodenum and jejunum. · The most characteristic imaging finding of celiac disease is reversal of jejunal and ileal fold patterns. Normally, the jejunum has more and closer together folds compared to the ileum. However, in celiac disease, the loss of jejunal folds due to villous atrophy causes a compensatory increase in the number of ileal folds. · Fluoroscopy small bowel follow-through may show flocculations of barium due to lack of contrast adhesion to the bowel wall due to villous atrophy. The moulage (French for casting) refers to a cast-like appearance of the featureless jejunum. · The CT findings of celiac disease include dilated, fluid-filled bowel loops, often with intra- luminal flocculations of enteric contrast. Reversal of jejunal and ileal fold patterns may be seen. Contrast can be seen both insinuated between the small bowel folds and centrally within the bowel, with a peripheral layer of low-attenuation secretions. Other CT findings of celiac disease include mesenteric adenopathy and engorgement of mesenteric vessels. · Unlike with other causes of enteritis, diffuse bowel wall thickening and ascites are less common. · An important complication of celiac disease is small bowel T-cell lymphoma, which may manifest as an exophytic mass, circumferential bowel wall thickening, or enlarged mesenteric lymph nodes. GI: 207 Celiac disease (continued) · Other complications of celiac disease include: Intussusception, thought to be due to uncoordinated peristalsis, without a lead-point mass. Pneumatosis intestinalis, thought to be due to dissection of intraluminal gas through the inflamed bowel wall. Pneumatosis in the setting of celiac disease is not thought to reflect bowel ischemia. Splenic atrophy. Increased risk of venous thromboembolism. Lab abnormalities include anemia (secondary to malabsorption), leukopenia, and immunoglobulin deficiency. Skin abnormalities include the characteristic dermatitis herpetiformis rash. Cavitating mesenteric lymph node syndrome (CMLNS) is a very rare complication of celiac disease. The central portion of affected lymph nodes become low attenuation due to liquid necrosis. CMLNS is thought to be highly specific for celiac disease when seen in combination with villous atrophy and splenic atrophy. The differential diagnosis of low attenuation mesenteric lymph nodes includes TB, Whipple disease, treated lymphoma, and CMLNS. Infectious enteritis · Several bacterial, viral, and fungal organisms may cause enteritis. · Yersinia and TB have a propensity to affect the terminal ileum, mimicking Crohn’s disease. · Salmonella is the most common cause of food-born gastroenteritis and causes segmental distal small bowel thickening on CT and segmental nodular thickened folds on fluoroscopy. Whipple disease · Whipple disease is due to infection by Tropheryma whippelii, which manifests in the GI tract as malabsorption and abdominal pain. Whipple disease may cause arthralgias and increased skin pigmentation. · Whipple disease characteristically causes low attenuation adenopathy that may appear similar to the cavitating mesenteric lymph node syndrome seen in celiac disease. · Radiographically, Whipple disease causes thickening and nodularity of duodenal and proximal small bowel folds. In contrast to celiac disease, there is typically no hypersecretion. Radiation enteritis Axial contrast-enhanced CT shows wall thickening of the distal ileum, most prominent in the deep pelvis, with hyperenhancement of the inner mucosa and mesenteric vessel engorgement. Although the findings are nonspecific, given the patient had recently completed radiation to the pelvis, this likely represents radiation enteritis. · Long-term effects of radiation to the pelvis include adhesive and fibrotic changes to the mesentery and small bowel. · Clues to the diagnosis of radiation enteritis include a history of radiation therapy and regional involvement of bowel loops not confined to a vascular territory and matching the radiation field. · Imaging findings include mural thickening and mucosal hyperenhancement (in the acute stages) with narrowing of the lumen (in the later stages). Radiation enteritis may be a cause of SBO. GI: 208 O Scleroderma · Scleroderma is a systemic disease characterized by the deposition of collagen into multiple internal organs and the skin. · The primary insult in the GI tract in scleroderma is impaired motility due to replacement of the muscular layers with collagen, which leads to slowed transit and subsequent bacterial overgrowth, progressive dilation, and pseudo-obstruction. · Radiographic findings are sacculations on the antimesenteric border (side opposite where the mesentery attaches) and a hidebound bowel due to thin, straight bowel folds stacked together. Graft versus host disease (GVHD) Axial (left image) and coronal (right image) contrast-enhanced CT shows diffuse wall thickening and mucosal hyperenhancement of jejunal and ileal loops, with associated mesenteric stranding and small volume ascites. · Graft versus host disease (GVHD) is a complication of bone marrow transplantation. The skin, liver, and GI tract are most commonly affected. · CT/MRI findings of GVHD include wall thickening with mucosal hyperenhancement and effacement of the normal small bowel fold pattern. The classic small bowel follow-through finding is the ribbon bowel (due to diffuse luminal narrowing by bowel wall thickening). Intestinal angioedema · Intestinal angioedema is a rare condition in which submucosal edema occurs secondary to extravasation of protein from vasculature. It may be seen with ACE inhibitor or angiotensin II receptor blockers use and hereditary C1-inhibitor deficiency. · Imaging findings include thickening of the bowel submucosa with possible straightening of bowel loops, mesenteric edema, and ascites. GI: 209 A Appendicitis Appendicitis: Coronal (left image) and axial (right image) contrast-enhanced CT shows a large focus of inflammatory stranding centered around the appendix in the right lower quadrant (yellow arrow). The margins of the appendix itself are indistinct and there is the suggestion of an early fluid collection (blue arrows). Note the two appendicoliths within the appendix (red arrows). · Appendicitis is the most common cause of acute abdomen. Acute inflammation of the appendix is thought to be due to obstruction of the appendiceal lumen by an appendicolith, fecal debris, or a mass, leading to venous congestion, mural ischemia, and bacterial translocation. · Appendicitis represents a spectrum of severity ranging from tip appendicitis (inflammation isolated to the distal appendix) to gangrenous/perforated appendicitis with abscess if the disease is not diagnosed until late. · For an adult with RLQ (right lower quadrant) pain and suspected appendicitis, CT is the preferred imaging modality. For a pediatric patient, ultrasound is first line. For pregnant women, ultrasound or MRI may be the most appropriate. · Imaging of appendicitis relies on direct and indirect imaging findings. · Direct ndings o appendicitis are due to abnormalities of the appendix itself: Distended, uid- lled appendi : 6 mm is used as cutoff for normal diameter of the appendix, although there is wide normal variability and 6 mm is from the ultrasound literature using compression. A normal appendix distended with air can measure >6 mm; therefore, some authors advocate using caution with a numeric cutoff in an otherwise normal-appearing appendix filled with air or enteric contrast. Appendiceal wall-thickening or hyperenhancement. Appendicolith, which may be a cause of luminal obstruction; however, appendicoliths are commonly seen without associated appendicitis. · Indirect ndings o appendicitis are due to the spread of inflammation to adjacent sites: Periappendiceal fat stranding. Hydroureter. Cecal wall thickening. Small bowel ileus. GI: 210  · On ultrasound, the key sonographic finding is a tubular, blind-ending, non-compressible structure in the right lower quadrant measuring >6 mm in diameter. It is generally necessary to use graded compression to evaluate for compressibility. Secondary findings of appendicitis can be evaluated by ultrasound, including free fluid and periappendicular abscess. · Chronic or recurrent appendicitis may cause clinical symptoms of appendicitis for weeks to even years and is often misdiagnosed. Imaging findings are very similar to those of acute appendicitis. Appendiceal neoplasms · Appendiceal neoplasms are uncommon (0.5–1.0% of appendectomy specimens) and most often present as acute appendicitis secondary to luminal obstruction (50%) by the mass itself. They may also present as intussusception, increasing abdominal girth, GI bleeding, and secondary genitourinary complications. · Carcinoid is the most common primary appendiceal neoplasm but is not as often detected on imaging. It is typically small and may be mass-like or demonstrate a diffuse infiltrative pattern. Carcinoid syndrome is present in only 5% of patients. Appendiceal carcinoid: Coronal (left image) and sagittal (right image) contrast-enhanced CT demonstrates a round enhancing appendiceal mass (yellow arrows) with associated dilatation and perforation of the appendiceal tip (red arrows). Patient underwent appendectomy with surgical pathology showing appendiceal carcinoid tumor. GI: 211 Appendiceal neoplasms (continued) · Mucinous neoplasms include a spectrum of entities ranging from mucocele, to low-grade mucinous neoplasm to mucinous adenocarcinoma. Pseudomyxoma peritonei may be a complication. Imaging most often shows a dilated, fluid-filled appendix, possibly with a soft tissue mass. If curvilinear mural calcification is present, the specificity is increased. Appendiceal mucocele: Sagittal T2-weighted (left image) and axial post-contrast T1-weighted (right image) MRI demonstrates a homogeneously T2 hyperintense, nonenhancing lesion (yellow arrows) arising from the tip of the appendix (red arrow). Axial contrast-enhanced CT image shows a well circumscribed, fluid filled structure arising from the base of the cecum with no significant solid component (arrow), found on pathology to be a low grade appendiceal mucinous neoplasm. · Non-mucinous adenocarcinoma is much less common. If seen on imaging, it appears as a soft tissue mass, not associated with a mucocele. GI: 212