Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

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Figure 2.4. Double pyloric channel (arrows). This patient had a prior antrectomy and the two channels were believed to be related to surgery.

Eosinophilic Gastroenteritis

Eosinophilic gastroenteritis is an inflammatory disorder of unknown etiology, considered to be a separate entity from idiopathic hypereosinophilic syndrome, although transitional forms probably exist. Its primary feature is eosinophilic infiltration of discrete or diffuse gastrointestinal tract segments. An occasional patient has eosinophilic infiltration of most if not all of the bowel. About half of these patients have some type of allergy, and a majority have peripheral eosinophilia.

Gastric involvement manifests most often as a narrowed lumen or thickened rugae.

In a rare infant eosinophilic gastroenteritis mimics the clinical findings and US appearance of idiopathic hypertrophic pyloric stenosis.

Eosinophilic gastroenteritis should be differentiated from helminth infestation with its associated eosinophilia.

Crohn’s Disease

Prevalence of gastric involvement in Crohn’s disease is unknown. When Crohn’s disease is evident in the upper gastrointestinal tract,

nearly always concomitant small bowel or colonic involvement is also found.

Although chronic gastritis and duodenitis are common in Crohn’s disease patients, only an occasional biopsy yields granulomas (12). One should keep in mind that granulomas are not pathognomonic for Crohn’s disease; they are also found in sarcoidosis, some infections such as tuberculosis and anisakiasis, as a foreign body reaction, or as an occasional vasculitis. As a practical matter, however, if other causes of granuloma formation are excluded, the presence of noncaseating granulomas is assumed to be due to Crohn’s disease.

The imaging appearance of gastric Crohn’s disease varies from aphthae to strictures (Fig. 2.5). Scintigraphy in Crohn’s patients with nonobstructive disease and no evidence of gastroduodenal disease shows normal gastric emptying, although symptomatic Crohn’s patients develop delayed gastric emptying.

Malacoplakia

Malacoplakia is a granulomatous inflammatory disease involving either the gastrointestinal or genitourinary tract. It is discussed in more detail in Chapter 10.

Malacoplakia is rare in the stomach. It originates either in the gastric wall or adjacent structure and infiltrates the stomach. Its primary significance is that it mimics a neoplasm.

Cytomegalovirus

The prevalence of acute viral gastritis is unknown. The most common is cytomegalovirus infection, which is encountered mostly in immunocompromised individuals and occasionally in children, where it tends to present as thickened rugae similar to Ménétrier’s disease.

Anisakiasis

Anisakiasis is caused by eating raw fish infected with Anisakis larvae. Many reports originate from Japan, but the condition is also encountered in other countries having an acquired culinary taste for raw fish such as sushi and sashimi. Ingestion of undercooked microwaved fish is also implicated. It is uncommon in older individuals and those with prior gastric surgery; rel-

ative achlorhydria appears to decrease larval toxicity.

Anisakiasis manifests by abdominal pain, at times severe enough to mimic an acute abdomen, shortly after eating infected raw fish. Eosinophilia is not common during the acute episode. Imaging detects gastric wall edema persisting for 1 or 2 days after infection. With a technically excellent double-contrast examination, a small moving curvilinear defect is identified on the mucosa.

Endoscopy identifies larvae adhered to gastric or duodenal mucosa.

Syphilis

Gastric syphilis is mostly of historical interest. It generally follows an indolent course. The gastric wall is infiltrated and thickened, at times suggesting a neoplasm. Histologically, a vasculitis is common.

On a barium study gastric syphilis mimics peptic ulcer disease or even a malignancy. Endoscopy and at times even histology suggest a gastric lymphoma or lymphocytic gastritis.

Tuberculosis

Most patients with gastric tuberculosis also have pulmonary involvement, although primary

gastric tuberculosis does exist, especially in Third World countries. Grossly it mimics sarcoidosis and Crohn’s disease. Some patients develop gastric ulcers, gastric outlet obstruction, or even massive hemorrhage.

The diagnosis can be established by histology and growth of Mycobacterium tuberculosis in an appropriate culture medium.

Histoplasmosis

Most patients with gastrointestinal histoplasmosis are immunocompromised or suffer from disseminated disease.

One patient with African histoplasmosis (Histoplasma duboisii) presented with a gastric ulcer that radiologically and endoscopically suggested a malignancy (13).

Emphysematous and

Phlegmonous Gastritis

Gastric pneumatosis and gastric emphysema are descriptive terms for gas in the stomach wall and emphysematous gastritis signifies inflammation, although these terms are used interchangeably to describe gas in the stomach wall. Some use emphysematous, phlegmonous, and necrotizing gastritis interchangeably,

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although these terms have different meanings and define different conditions.

Emphysematous gastritis is a rare finding. Involvement ranges from focal to most of the stomach being involved.

Etiologies leading to gas in the stomach wall are listed in Table 2.2. Gastric ischemia as a cause of emphysematous/phlegmonous gastritis is rare except in patients who have had prior extensive surgical gastric devascularization. Rarely, phlegmonous gastritis develops after nongastric surgery (14). Gastric emphysema occasionally develops in a neonate with duodenal obstruction and not due to necrotizing gastritis. Transient gastric emphysema was associated with colonic infarction (15). Some patients with emphysematous gastritis are relatively asymptomatic, and in this subgroup emphysema presumably is neither infectious nor ischemic in origin.

The diagnosis is suggested by imaging and not by endoscopy. Inflammation, edema, and gas develop in the submucosa and deeper layers, with the overlying mucosa being relatively

Table 2.2. Etiologies of emphysematous gastritis

normal. Conventional radiography and CT reveal linear or oval gas collections in the gastric wall. Focal emphysema is better seen with CT than conventional radiography. Ultrasonography reveals focal emphysema as hyperechoic foci with distal reverberations.

Ischemia

Gastric ischemia is discussed in Chapter 17. Overt gastric ischemia is rare. Symptoms tend to be nonspecific, especially with a gradual onset.

Radiation

The stomach is relatively resistant to radiation damage. Deep ulcers have developed months after radiation to adjacent nodes. These ulcers tend not to heal.

Ménétrier’s Disease

Ménétrier’s disease is one of the protein-losing enteropathies. Clinically, hypoproteinemia is evident and if untreated leads to edema. Fecal a1-antitrypsin excretion is increased and serves as a marker for protein-losing enteropathy.

Imaging findings consist of marked rugal and gastric wall thickening. Initially the antrum is spared, but eventually the entire stomach becomes involved. Imaging often suggests a malignancy, such as lymphoma. Complicating the issue further is that occasionally Ménétrier’s disease undergoes malignant transformation.

A type of Ménétrier’s disease occurs in children.Although these children do have a proteinlosing enteropathy and gastric rugae are thickened, the condition is transient and probably differs from that seen in adults. Primary cytomegalovirus infection is evident in some children with such a transient form of Ménétrier’s disease.

In adults, US reveals mucosal thickening with normal submucosa and muscle layers. In children, US is useful in following disease progression and resolution.

Sarcoidosis

Gastric involvement without systemic sarcoidosis and no lung hilar adenopathy is rare.At times

Figure 2.6. Antral sarcoidosis.The antral lumen is narrowed and folds thickened by a diffuse antral wall infiltrate (arrows).

gastric biopsies yield epithelial cell granulomas, even though imaging identifies no abnormality.

Once established, gastric sarcoidosis manifests as nodules, thickened folds, gastric wall thickening, lumen narrowing, and superficial antral ulcers (Fig. 2.6); the condition thus mimics Crohn’s disease and linitis plastica, although a similar appearance is also seen in gastric syphilis, eosinophilic gastritis, polyarteritis nodosa, and phlegmonous gastritis. Rarely, a focus of sarcoid infiltration develops a deep ulcer.

Gastric carcinoma and lymphoma have developed in a setting of gastrointestinal sarcoidosis; whether these associations are fortuitous or not is conjecture.

Amyloidosis

Amyloidosis is probably a blood dyscrasia. It occurs in a primary form and in association with such diseases as chronic infections and multiple myeloma.

Most often gastric amyloidosis leads to diffuse antral wall thickening, at times narrowing the lumen to the point of obstruction. A patient with familial amyloid polyneuropathy had multiple gastric amyloid polyps (16). A patient on hemodialysis and secondary amyloidosis developed phlegmonous gastritis (17).

Endoscopic US reveals gastric wall thickening and loss of normal mucosal and submucosal outline.

Tumors

Bezoars

Gastric bezoars are more common after prior gastric surgery or peptic ulcer disease than in the general population.

Trichobezoars lead to pain, vomiting, and bleeding due to erosions. If sufficiently large, they result in gastric obstruction, or, if they pass into the small bowel, small bowel obstruction. Some trichobezoars extend from the stomach, through the small bowel, to the colon (Rapunzel syndrome). Iron deficiency anemia is not uncommon.

Most small trichobezoars are readily diagnosed by conventional radiographically and CT. Some trichobezoars are associated with gastric pneumatosis. Their MRI appearance varies depending on relative amounts of gas and fluid; the presence of air causes a hypointense appearance both on T1and T2-weighted images, whereas fluid and other debris result in a hyperintense appearance on T1and T2-weighted images. It is the larger ones that fill almost the entire gastric lumen that cause a diagnostic dilemma. If in doubt, a barium study is diagnostic.

Because of their consistency, trichobezoars are difficult to remove endoscopically and, especially with larger ones, surgical removal is necessary. Most large gastric phytobezoars are treated surgically, although an occasional one is fragmented endoscopically.

Numerous preparations result in gastric pharmacobezoars, ranging from aluminum hydroxide gel to enteral feeding formulas. Some pharmacobezoars also cause symptoms secondary to continued intragastric release of their active ingredients.

Nonneoplastic Tumors

Cyst

Most small gastric cysts are nonneoplastic and represent intramural collections of gastric secretions. They range from submucosal cystic glands and duplication cysts to cystica polyposa, with an occasional hamartoma and adenomyoma. Their intraluminal projection varies. Some gastric cysts cannot be readily classified.

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Cystica polyposa is an uncommon solid and cystic gastric tumor, with most developing proximal to a gastroenterostomy. Their prevalence increases with time after surgery. These tumors consist of epithelial hyperplasia and dysplasia and contain dilated gastric glands that are either limited to the mucosa (gastritis cystica superficialis) or extend into the submucosa (gastritis cystica profunda). Large and mostly intraluminal ones have led to gastric outlet obstruction.

An unclear relationship exists between cystica polyposa and cancer developing in a gastric stump.

Hyperplastic Polyp

A prospective gastroscopy study of resected polyps found 55% to be hyperplastic polyps, 29% inflammatory, and 10% adenomatous (18); other, less common, polyps included fundic gland polyps,carcinoid,early gastric cancer,and a pancreatic rest. All of these polyps were smaller than 2cm.

Most hyperplastic polyps are discovered incidentally, and are small (less than 20mm in diameter), smooth, and multiple, and most are found in the antrum. Occasionally hyperplastic polyps enlarge and become lobulated, and their appearance suggests a polypoid carcinoma (19). Whether to simply biopsy these large polyps is debatable; most are resected.

Hyperplastic polyps are usually considered nonneoplastic per se, although some contain dysplasia, carcinoma-in-situ, or even a carcinoma. Pedunculated antral hyperplastic polyps can prolapse into the duodenum. Hyperplastic gastric polyposis is associated with colorectal adenomas. The relationship between hyperplastic polyps and nonfamilial fundic gland polyposis is not clear but these appear to be distinct entities (fundic gland polyps are discussed later; see Nonfamilial Polyposis).

Inflammatory Fibroid Polyp

Inflammatory fibroid polyps are nonencapsulated submucosal lesions composed primarily of loose connective tissue and inflammatory tissue. They also contain varying amounts of myofibroblasts, thus confusing the histologic picture. They occur throughout the gastroin-

testinal tract; in the stomach they predominate in the antrum.

Most smaller polyps are sessile and are covered by smooth overlying mucosa, whereas larger ones tend to project more intraluminally, ulcerate and bleed (Fig. 2.7). Prolapse into the duodenal bulb leads to gastric outlet obstruction. Endoscopic biopsies tend to be noncontributory, and a polypectomy is necessary for diagnosis.

Endoscopic US of 10 proven gastric inflammatory fibroid polyps showed all to be located in the second and/or third sonographic layer, 90% had an indistinct margin, 80% were hypoechoic, and 90% were homogeneous in appearance (20).

Inflammatory Pseudotumor (Fibrosarcoma)

A so-called inflammatory pseudotumor, also known as plasma cell granuloma, inflammatory fibrosarcoma, and other terms, is a rare, infiltrating condition of unknown etiology. Although included here under nonneoplastic tumors, whether it is indeed inflammatory or

Figure 2.7. Inflammatory polyp in distal antrum. An adenoma has a similar appearance.

represents a neoplasm is not settled. This condition is discussed in more detail in chapter 14.

A number of these tumors are associated with elevated sedimentation rate. In the stomach they ulcerate and bleed.

Heterotopic Pancreas

ADVANCED IMAGING OF THE ABDOMEN

Hemangioma

For unknown reasons gastric hemangiomas are rare. Most have manifested by bleeding. They appear similar to other mesenchymal tumors. Several have contained phleboliths, which aid in diagnosis. An occasional one is polypoid.

Ectopic pancreatic tissue occurs at a number of sites, being most common in the gastric antrum and proximal duodenum, with only an occasional jejunal one found. Histology reveals either complete pancreatic tissue or exocrine pancreas, with only an occasional one consisting mostly of endocrine pancreas. Although often considered innocuous, complications of such ectopic tissue include inflammation, cyst formation, adenocarcinoma transformation, and formation of an endocrine tumor. Pancreatic acinar-appearing cells are occasionally found in gastric mucosa; such metaplasia is often detected around the squamocolumnar junction and differs from ectopic pancreatic tissue.

Ectopic antral pancreatic tissue usually presents as a single submucosal tumor, occasionally up to 3cm in size. A central umbilication is identified in some.

A common CT appearance is an oval or round tumor containing smooth or serrated margins. About half enhance with contrast similar to normal pancreas (21,22); poorly enhancing ones contain mostly ducts and muscle tissue, with pancreatic acini being sparse. A minority contain a dilated heterotopic pancreatic duct. Of interest is that the CT findings are often interpreted incorrectly as representing other lesions.

Gastric heterotopic pancreatic tissue even led to a pseudocyst.

Teratoma

The stomach is a rare site for a teratoma. These tumors occur primarily in males and often present as bulky, palpable, abdominal masses. They range in location from primarily intraluminal, to intramural, to extrinsic.

Computed tomography and MR are the preferred imaging modalities, identifying both cystic and fatty components and often also suggesting its gastric origin.

Extramedullary Hematopoiesis

A barium study in a patient with myelofibrosis revealed multiple gastric polyps (23); biopsy identified extramedullary hematopoiesis in these polyps, a very rare site for hematopoiesis.

Benign Neoplasms

Adenoma

Gastric adenomas are uncommon. Most occur in the antrum. The two most common presentations are bleeding or malabsorption.

Adenomas are at increased risk of malignant transformation and even an occasional small adenoma contains a carcinomatous focus. Also, the presence of an adenoma is associated with an increased risk of developing a gastric carcinoma elsewhere in the stomach. Gastric villous adenomas are associated with synchronous rectal villous adenomas. Probably an association also exists between gastric adenomas and other colonic polyps.

Nonneoplastic polyps and most adenomas have a very similar imaging appearance and most smaller ones are sessile (Fig. 2.8). In a collection of atypical adenomas, four were depressed and three were flat, they were located around the incisura or antrum, they ranged from 10 to 25mm in diameter, and with a barium study all mimicked an early gastric carcinoma (24); a nodular surface, convergency of folds, and a shallow depression were common.

Solid polyps are homogeneous and hypointense on T1and hyperintense on T2weighted MRI (except for lipomas, as discussed below).

Leiomyoma

Gastric leiomyomas are common; a majority are discovered incidentally, often in a stomach resected for other reasons, and are small in size.

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Figure 2.8. Antral adenoma appearing as a sessile polyp (arrow).

They are more common in the fundus than more distally.

For some of these tumors a distinction between leiomyoma and its sarcomatous counterpart is tenuous at best and some are thus labeled as having a variable biologic patterns or simply as gastrointestinal stromal tumors (GISTs) (stromal tumors are discussed in more detail in Chapter 1).

With growth, both benign and malignant ones tend to outgrow their blood supply and become partially necrotic (Fig. 2.9); as a result the larger ones have a heterogeneous, partly

Figure 2.9. Ulcerated antral leiomyoma (arrows). (Courtesy of Arunas Gasparaitis, M.D., University of Chicago.)

necrotic-cystic imaging appearance. A rather prominent contrast enhancement is common in nonnecrotic regions.

Calcifications in a gastric leiomyoma are rare (25) and ossification even rarer.

Lipomatous Tumors

Most gastric lipomatous tumors are lipomas, with an occasional angiolipoma, teratoma, or even a liposarcoma found. Reactive lipomatosis is a nebulous entity encountered occasionally.

Most lipomas are discovered incidentally, most often in the fundus. An occasional one ulcerates, presumably secondary to ischemia, and bleeds. An occasional prepyloric lipoma obstructs or, if polypoid, prolapses into the duodenum and leads to bleeding. Occasionally multiple gastric lipomas are detected.

Barium studies reveal most lipomas as smooth submucosal tumors with or without ulcerations, similar to stromal tumors and lymphomas (26). Computed tomography reveals lipomas to be of homogeneous density of about -30 to -100 Hounsfield units (HU); some have an apparent capsule. Similar to other structures containing fat, lipomas are hyperintense on T1and hypointense on most T2-weighted images and they lose signal intensity on fat-suppressed T1-weighted spoiled gradient echo (SGE) images. Thus, regardless of location, a lipoma can be distinguished from most other polyps. Distinguishing a lipoma from a liposarcoma, on the other hand, is problematic. Well-differentiated liposarcomas contain thick septa or nodules on T1-weighted MRI, with these septa or nodules becoming hyperintense on fat-suppressed or STIR T2-weighted sequences, findings seen only in a minority of lipomas (27). A heterogeneous appearance or presence of a necrotic or cystic component in a fat-containing tumor should suggest a teratoma or a liposarcoma.

The rare angiolipoma shows marked CT contrast enhancement.

A heterogeneous appearance or presence of a necrotic or cystic component in a fat-containing tumor should suggest a teratoma or a liposarcoma.

Hemangiopericytoma

Hemangiopericytomas can occur in most tissues, but a gastric location is rare.

Polyposis Syndromes

Gastrointestinal polyposis syndromes are discussed in more detail in Chapter 4. Included here are only those aspects pertinent to the stomach.

Nonfamilial Polyposis

(Fundic Gland Polyps)

Fundic gland polyps are most prevalent in middle-aged women and are not associated with either gastric adenomas or gastric cancers; they can grow or regress, some even resolving completely. They are not premalignant.

They tend to be small, ranging in size from 1 to 3mm. A double-contrast upper gastrointestinal study readily detects these polyps.

malignancy or control of protein-losing gastropathy.

Cronkhite-Canada Syndrome

These patients develop characteristic ectodermal abnormalities consisting of dystrophic nail changes and alopecia.

A barium study reveals multiple polyps scattered in the stomach, duodenum, and small bowel. Biopsy of these polyps shows mostly an inflammatory infiltrate and a cystic component. Some of these patients have an elevated carcinoembryonic antigen (CEA) level that decreases after steroid therapy.Anecdotal reports describe bowel adenomas.

Familial Polyposis

Upper gastrointestinal polyps are common in a setting of familial adenomatous polyposis. These polyps are either of gastric fundic gland origin (hyperplastic) or adenomas. Most resultant gastric adenocarcinomas arise from adenomas, although a rare adenocarcinoma originates from a hyperplastic fundic polyp.

Occasionally gastric polyps in patients with familial adenomatous polyposis regress on indomethacin therapy.

Peutz-Jeghers Syndrome

Gastric hamartomatous polyps develop in patients with Peutz-Jeghers syndrome. Occasional gastric adenocarcinomas have been reported.

Juvenile Polyposis

Gastric juvenile polyposis, consisting of numerous juvenile polyps scattered throughout the stomach, is rare. Some patients have a family history of intestinal polyposis or have generalized juvenile polyposis, although it is not clear whether gastric juvenile polyposis is a separate entity from generalized juvenile gastrointestinal polyposis.

These polyps predominate in the antrum; with time, some became numerous, larger, and pedunculated. They are associated with adenomas and adenocarcinomas. Eventual gastrectomy is performed either for suspected

Adenocarcinoma

Adenocarcinomas involving the gastroesophageal junction are discussed in Chapter 1. Both clinically and from prognostic and management viewpoints these tumors are closer to esophageal cancers than to more distal gastric cancers. Early gastric cancers are discussed below. Although these tumors are adenocarcinomas and are precursors to more advanced cancers, their clinical presentation and imaging approach are sufficiently different to warrant a separate discussion.

Diffuse scirrhous gastric tumor spread leads to a linitis plastica appearance (Fig. 2.10). Some use the term linitis plastica as a synonym for an extensive scirrhous gastric adenocarcinoma, but this term is a descriptive one; several other disorders can have a similar appearance: metastatic carcinoma (breast, etc.), lymphoma, sarcoidosis, prior corrosive ingestion, and even gastric syphilis. Also, at times H. pylori gastritis and other benign entities thicken the gastric wall sufficiently to suggest a cancer.

Clinical

The prevalence of gastric cancer, by age, varies considerably throughout the world. In the Far East, gastric cancer is more common in a younger age group than in Europe or North America and their 5-year survival rate is similar to other age groups. On the other hand, gastric cancer in younger American patients is more likely to be associated with distant metastases