Diseases of the Stomach and Duodenum:Basics of Radiologic-PathologicCorrelation

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Introduction

The purpose of this workshop is to apply basic principles of radiologic-pathologic correlation to the differential diagnosis of diseases of the stomach and duodenum. Tumors and inflammatory or reactive processes will be empha- sized and used as illustrative examples in the syllabus.

The stomach and duodenum are violent places, with hos- tile pH levels and endocrine and exocrine glands with feed- back loops that are in constant battle. The end result is that both are prone to diseases of excess acid or alkali, or diseases of diminished resistance to these caustics. In addition, hormonal influences affect the structure and function of stomach and duodenum; gastrin is the most famous hor- mone associated with the stomach. In addition to stimulat- ing gastric parietal cell acid production, gastrin also stimulates all neuroendocrine glands of the alimentary tract to some degree. Carcinoid glandular hyperplasia of the stomach occurs with high persistent gastrin levels, as seen in Zollinger Ellison Syndrome, atrophic gastritis, and with acid suppression medications. Recent controversy has arisen about the possible relationship of acid suppression therapy with hyperplastic gastric polyps and atrophic gastritis.

‘Radiologic-pathologic correlation’ employs knowledge of pathological processes (along with physiology and anatomy) for the analysis of radiologic abnormalities to enhance differential diagnosis [1, 2]. The dictionary defines pathology as: ‘The study of the essential nature of diseases and, especially, the structural and functional changes produced by them.’ In this sense, the radiologist is truly a pathologist who sees the changes in vivo, when there is still an opportunity to intervene.

It is common teaching practice to classify disease by pathologic diagnoses. In practice, the patient seldom pre- sents with a known diagnosis, but with non-specific com- plaints. Diagnosis is suggested by analyzing morpholog- ic changes seen radiologically. Incorporating knowledge of pathology with clinical information should aid in the formation of a rational differential diagnosis, while avoiding rote memorization of exhaustive lists and

‘gamuts’. Pathologic correlation is especially useful in the gastrointestinal (GI) tract where diagnosis depends

heavily on determining the layer of the bowel wall involved, and on patterns of filling defects, strictures, fold abnormalities and ulcers.

Normal Structure

A brief review of normal bowel structure may aid in the appreciation of pathologic alterations. The bowel varies in structure and function from region to region, but many anatomic features are common throughout. The gut is a stratified tube that is organized into four main layers: mucosa, submucosa, muscularis and an outer adventitial covering (Fig. 1, 2).

The mucosa, in turn, has three layers. The luminal lining of squamous or columnar epithelial cells provides a protective surface involved in absorption and mucus production. The lamina propria is a supportive layer of mesenchyme containing capillaries and nerves. A thin layer of smooth muscle, the muscularis mucosae, separates the mucosa from the submucosa. Lymphoid follicles tend to lie near, or bridge across, the muscularis mucosae.

The submucosa is a layer of soft fibroconnective tissue containing the main blood vessels, lymphatics and nerves that supply the mucosa. The main muscular wall, the mus-

IDKD 2006

Diseases of the Stomach and Duodenum: Basics of Radiologic-Pathologic Correlation

J.E. Lichtenstein¹, F.J. Scholz²

1Department of Radiology, University of Washington Medical Center, Seattle, WA, USA

2Department of Radiology, Lahey Clinic Medical Center, Burlington, MA, USA

Fig. 1. Diagram of an idealized cross-section of normal bowel showing the major components found in the upper GI tract

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cularis propria, generally has an inner circular and outer longitudinal layer. Auerbach’s autonomic nerve plexus, which controls peristalsis, is located between the two layers. ‘Adventia’ is a general term for whatever surrounds the gut. Much of the GI tract is surrounded by delicate fi- brofatty mesenchyme supporting a continuous thin fibrous layer, the serosa. The esophagus and retroperitoneal portions of the duodenum and colon lack a defined serosa.

The continuity of the adventia with surrounding tissue can facilitate spread of inflammatory and neoplastic disease.

Morphology of Lesions

The radiographic morphology of lesions almost always gives important clues about the pathologic diagnosis (Fig.

3, 4). Overgrowths of the luminal surface epithelium can cause hyperplasias, adenomas, or carcinomas, depending on the degree of histologic atypia. Epithelial polyps and tumors tend to protrude into the lumen, have irregular surface texture, form acute angles with the surrounding surface, and usually do not displace the centerline of the gut unless they become quite large. Benign lesions tend to grow slowly, are often small, rounded and, if growing into the lumen, have time to be drawn out onto stalks by peristaltic action. Aggressive lesions spread out and involve adjacent structures. They are likely to be broad-based and tethered to deeper mural structures. They become large more rapidly and are more likely to outgrow their blood supply and become necrotic. Non-uniform, multi-centric growth tends to cause irregular contours and lobulation.

Any of the subepithelial mesenchymal tissues may lead to benign or malignant overgrowths, the malignant forms being termed sarcomas. Submucosal lesions also tend to grow toward the lumen, being restrained by the firm, rubbery muscularis propria. The displaced mucosal surface tends to be smooth with obtuse angles at the edges. Masses Fig. 2. Diagram showing representative features seen in photomi-

crographs of normal bowel. Relative proportions and details of ep- ithelium vary with organ and location. (LF, lymphoid follicle; AP, Auerbach’s autonomic myenteric nerve plexus; MP, Meissner’s submucosal nerve plexus)

Fig. 3. Drawings of classic effects of masses on bowel which are de- termined by location of lesion: extrinsic (top), submucosal (mid- dle), and mucosal (bottom)

Fig. 4. Drawings of strictures illustrating classic distinction between smoothly tapered benign process on left and abrupt-edged, irregular-surfaced, malignant lesion on right

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arising in the muscle wall (e.g., gastrointestinal stromal tumors (GISTs), leiomyomas and leiomyosarcomas) may grow either towards the lumen (endoenteric) or away from it (exoenteric), or in a combination of patterns. Extrinsic masses sometimes bulge into the lumen, but they typically have very obtuse angles at the margins and tend to displace the lumen centerline earlier than intrinsic lesions.

Hamartomas are mixed arrangements of otherwise normal tissues. They are generally benign and usually contain both epithelial and mesenchymal elements.

Most strictures result from scarring or from cellular infiltration. With scarring, the narrowing has smooth margins, whereas with infiltration, the contour depends on the nature of the process and its location within the wall. Healing of many types of injury results in scarring and stricture formation. Strictures from widespread inflammation, as in caustic ingestion or radiation, are likely to be elongated. When the injury is old and the epithelium has healed, the luminal surface will be smooth with tapering edges (Fig. 4).

Irregularity of the luminal surface of a stricture indi- cates involvement of the epithelium. It may be caused either by ulceration or a primary epithelial process such as carcinoma, the infiltration of which produces the stricture. Frequently the stricture is caused more by fibrous reaction to the tumor cells than by the mass of neoplastic cells per se. Mucin-producing adenocarcinoma is espe- cially likely to exhibit this tendency. Benign strictures are often long and smoothly tapered, whereas malignant strictures tend to produce focal, relatively short, irregular strictures with abrupt edges.

Strictures may be due to compression by extrinsic en- circling masses. While uncommon in the stomach, annular pancreas provides a classic example in the duodenum (Fig. 5) [3]. The mucosa and submucosa are unaffected except for being smoothly stretched over the lesion, pro- viding a smooth contour.

Dilatation in hollow peristaltic organs occurs either be- cause of distal obstruction or because of intrinsic neural, or muscular, abnormality. Excluding a mechanical obstruction, the most common cause of dilatation is ady- namic ileus. The precise mechanism is often unclear. It can result from local irritation, apparently involving the autonomic nerve plexi in the bowel wall. Dilatation caused by intrinsic structural changes in the bowel is relatively uncommon. Achalasia is a classic prototype in which deficiency of ganglion cells in Auerbach’s plexus of the esophagus results in hypotonia and progressive dilatation. Gastroparesis from diabetic neuropathy and smooth muscle atony and atrophy in scleroderma (progressive systemic sclerosis) due to collagen vascular disease are other examples.

Thickening of the mucosal folds lining the gut is a com- mon pattern, especially in the stomach and duodenum.

Inflammation is very common but the radiographic find- ings, such as spasm and irritability, and fold irregularity and

54 J.E. Lichtenstein, F.J. Scholz

thickening are often non-specific and difficult to distinguish from normal variation when relatively mild. Erosions through the epithelium that do not breach the muscularis mucosae, separating the mucosa from the submucosa, may be detected with double contrast barium technique (Fig. 6).

Aphthous lesions suggest granulomatous disease, especially Crohn’s disease, but are not specific.

Hyperplasia of normal structures, or infiltration or de- position of cells or foreign material may cause thickening.

Examples of diffuse epithelial overgrowth include Menetrier disease in which gastric fundal folds are markedly thickened by proliferation of the superficial mucus-producing cells (Fig. 7). Zollinger-Ellison Syndrome is another classic example in which an ectopic gastrin source stimulates gastric acid production and marked hyperplasia of parietal cells in the deep mucosal glands of the gastric fundus. Excess fluid is found with both entities, but inflammation and ulcers due to excess acid are found only in Zollinger-Ellison Syndrome. Both of these conditions are classically distinguished from other inflammatory disease in which fold thickening is usually more distal.

Ulcers are holes in the normal protective epithelial barri- er lining the gut. They result in protrusions of contrast be- Fig. 5. Annular pancreas causing smooth, concentric, compressive narrowing of descending duodenum

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yond the expected margin of the lumen of the organ. They may be caused by noxious agents in the bowel lumen or by insults such as mucosal ischemia or inflammation in the mucosa itself. Infection with Helicobacter pylori is now recognized as the etiology for most upper GI tract ulceration. Once the surface is breached, the erosion can extend more deeply. In a benign ulcer, the surrounding epithelium remains relatively resistant and intact, although inflamed. Destruction of the less resistant submucosa undermines mucosa, which tends to overhang the crater edge. The firm, rubbery muscularis mucosae is relatively resistant and forms a temporary barrier. The re- sulting flat-bottomed defect has narrow communication with the lumen and a characteristic ‘collar button’ shape.

Surrounding mucosal folds extend all the way in to the edge of the ulcer.

In contrast, adenocarcinoma typically produces a nodu- lar, irregular epithelium. An ulcer in this surface has irregular edges that tend to be eroded along with underly- ing tissue without undermining. Erosion into an extensive tumor mass produces an irregular, saucer-shaped hole rather than a flat bottom. Ulceration into a submucosal tumor such as a GIST or lymphoma nodule produces a vari- ably shaped crater, but because the epithelium is not pri- marily involved, its edge is often sharply defined.

Tumors are usually seen as combinations of filling de- fects and strictures. Carcinoma is, by definition, an epithelial lesion. Its mucosal origin is generally reflected by the presence of ulcers and luminal nodules. Its poor prognosis can be explained, in part, by a propensity for sub- Fig. 6. Erosive gastritis. Air contrast barium upper GI study show-

ing contrast pooling in multiple shallow gastric erosions surrounded by lucent edema

Fig. 7. Menetrier disease. CT showing grossly enlarged gastric folds in the fundus due to hyperplasia of secretory cells in the superficial layers of the mucosa

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mucosal extension and for spread through the wall.

Benign hyperplastic and adenomatous tumors also arise in the epithelium and this is reflected in their roentgen appearance, often allowing their differentiation. Other tumors arise in the submucosal mesenchyme. Many of these are slow growing and benign. They present radi- ographically as rounded intramural lesions with smooth overlying mucosa. As such lesions become large, however, the epithelium may ulcerate.

The normal histologic components vary with the region of the gut and so do their tendencies for pathologic growth. One must know the local ‘track record’ for suc- cessful prediction. For example, the stratified squamous esophageal epithelium commonly transforms to squamous cell carcinoma after long exposure to smoke and alcohol.

Flat, glandular, columnar epithelium frequently becomes metaplastic, leading to adenocarcinoma at the esopha- gogastric junction, but only rarely does so in the small bowel. Solid mural tumors of the esophagus are likely to be benign spindle-cell, stromal tumors, regardless of their size. Similar lesions in the stomach are likely to be malignant, especially if larger than a few centimeters. Polyps in the duodenum are likely to be hyperplasias of Brunner’s glands or hamartomas including pancreatic tissue. Those entities would be rare elsewhere and similar gross morphology would prompt different considerations.

Malignant Gastric and Duodenal Tumors

Adenocarcinoma

Gastric carcinoma is decreasing in frequency in Western counties and duodenal carcinoma is rare. By the time they become markedly symptomatic, the tumors are often advanced and beyond cure. The role of the radiologist at that point is to locate and stage the tumor. However, radiographic studies performed for other reasons provide the potential for detection of asymptomatic early gastric carcinoma.

Sometimes epithelial malignancies grow into the lumen as a mainly cellular mass of tissue with little fibrosis.

Such a lesion is more often well-differentiated. Typically, the surface is lobulated or ulcerated, as opposed to the usually smooth surface of benign lesions (Fig. 8).

Mucin-producing tumors have a tendency to infiltrate widely and incite a great deal fibrotic reaction. Fold thickening may result, and often the wall is thickened and appears stiff and constricted, producing the classic

‘leather bottle’ appearance. The lesion may extend around the lumen in an annular manner (Fig. 9) [4, 5].

Other Malignancies

Lymphoma is a mesenchymal process, but has many possible appearances. Typically lesions are lobulated. The mucosa may be intact until late, but ulceration into the soft, cellular tumors is often extensive.

Fig. 8. Multilobulated polypoid gastric adenocarcinoma growing in- to the lumen

a

b

Fig. 9. Infiltrating schirrous gastric carcinoma causing marked thickening and stiffening of the stomach and constricting the lu- men. a Single contrast barium upper GI. b CT of same case

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Metastases are frequently multiple but can have many appearances, depending upon the primary tumor and whether the lesions are submucosal or serosal. Metasta- sized breast cancer, in particular, has a tendency to re- semble sclerosing mucin-producing adenocarcinoma.

Kaposi sarcoma, a soft biphasic mixture of vascular and stromal tissue, tends to form rounded subepithelial nodules in the stomach of HIV positive patients.

Benign Tumors

The incidence of benign tumors is difficult to define since, if they are small or produce little effect on the lumen, they are often asymptomatic and escape attention.

They are relatively common among clinically evident tumors, but the absolute incidence is probably much high- er and probably exceeds that of malignancy [6].

Epithelial hyperplasias and adenomas may form sessile or pedunculated nodules. Adenomas are neoplastic, usually polypoid, excrescences due to proliferation of dysplastic epithelial cells. Excluding polyposis syndromes, they are usually solitary and are uncommon in the duodenum.

Villous tumors imply more severe dysplasia, with more aggressive growth. The lesions tend to be more sessile, larger, and have more irregular surface texture.

Barium trapped in the interstices of the villous surface gives a striated, reticulated, or ‘soap bubbly’ appearance (Fig. 10). In the duodenum they are usually found near the papilla and frequently harbor foci of carcinoma, especially if large [7, 8]. It is tempting to speculate that the dysplasia results from the irritating effect of bile or pancreatic secretions.

Mesenchymal tumors arise in the deeper layers. Thus, initially, their overlying epithelial layer of the mucosa is intact. The smooth luminal surface provides a convenient means of predicting the nature of such tumors (Fig. 11).

Other aspects of appearance depend upon the consisten- cy of the tumor tissue and its site of origin within the wall. Virtually any type of mesenchymal cell in the bowel wall may occasionally give rise to neoplastic or hamar- tomatous tumors, but only a very few occur frequently enough to warrant serious consideration.

Spindle Cell/Stromal Tumors

Gastrointestinal stromal tumors (GISTs) and leiomyomas are by far the most common benign mesenchymal tumors of the GI tract [9]. Leiomyomas are thought to usually arise from the smooth muscle of the wall. GISTs are now considered to arise from the interstitial cells of

a c

b

Fig. 10. Villous adenoma in proximal duodenum containing foci of adenocarcinoma. a, b Barium upper GI showing filling defect in lumen (arrows, a; arrowheads indicate tumor in duodenum). Irregular texture correlates with fronds of dysplastic surface epithelium.

c CT of same case

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Cajal, which are stem cells similar to the pacemaker cells of the bowel wall. They are characterized by ex- pression of a tyrosine kinase growth factor receptor, KIT (CD117). The pathologic criteria for malignancy in both smooth muscle cell tumors and GISTs are somewhat ar- bitrary. They depend upon averaging the number of mi- totic figures in multiple high power microscopic fields and assessing cellularity and pleomorphism [10, 11].

The tumors tend to grow slowly. Although often small and difficult to detect, occasionally such tumors may become huge.

Malignancy in stromal tumors correlates well with size, except in the esophagus where the vast majority are benign, even when very large. Stromal tumors tend to grow as firm, rubbery, rounded masses of compact intertwined bundles of spindle cells. The tumors have no true capsules but are usually easily shelled out from surrounding com- pressed tissue. Their roentgen appearance depends upon their site of origin, size and direction of growth.

Tumors arising in the outer layers of the wall tend to grow outward into the surrounding tissue. If small, they cause no symptoms and the majority are probably never detected. When larger, they may appear as extrinsic masses. Lesions arising on the inner aspect of the muscle wall or muscularis mucosae more easily displace the pli- able submucosa and mucosa than the firmer muscle wall.

Thus they grow toward the lumen and tend to cause symptoms relatively early. Ordinarily the epithelium is stretched smoothly over such submucosal masses, often with obtuse angles at the periphery. If such lesions become large enough, however, they may protrude into the lumen and develop short pedicles. In that case the mucosa will be tucked around the lesion with acute angles at the borders, a limitation of the so-called ‘sulcus sign’

sometimes used to distinguish mucosal from submucosal or extrinsic lesions. While the covering mucosa is initially intact, the protruding submucosal mass exposes it to trauma from luminal contents and may compromise its

blood supply. Superficial ulceration, thus, is an expected complication of any such lesion and may be its mode of presentation. Vascularity within GISTs and smooth muscle lesions is variable, often being rather sparse.

Frequently, however, there are prominent arteries in the superficial layers of such tumors and these can be the source of sudden, dramatic hemorrhage when eroded by ulcers. Such behavior is well known with gastric GISTs where the luminal acid is ulcerogenic and where the lesions can become larger without luminal compromise.

GISTs are usually solitary, but may also be multiple in a small number of cases. Calcification is rare in GI tract leiomyomas, as opposed to the situation in the uterus.

When it occasionally occurs, it can be a useful radiographic clue to the diagnosis.

Lipoma

Lipomas are rare, uniformly benign, localized prolifera- tions of submucosal fat. Like leiomyomas, they grow by slow compression of surrounding tissue and usually no true capsule can be defined. Their soft texture and submucosal origin dictate that the tumors grow almost en- tirely into the lumen with relatively little effect on the muscle wall. As they become large they may form pedunculated, intraluminal, polypoid masses and may cause intussusception. The overlying mucosa is initially intact but may eventually breakdown and ulceration is one means of presentation. Their low X-ray attenuation allows a confident diagnosis on computed tomography (CT) (Fig. 12).

The Duodenum

The duodenum, although subject to the above generali- ties, is one of the most unique and dynamic parts of the body [12-16]. It has both intra- and retro-peritoneal portions. Being centrally located in the abdomen, it is often affected by diseases in neighboring organs. It is a battle- ground of acids and alkalis relating to drainage from three of the body’s major sources of digestive chemicals:

the liver via the biliary tree; the pancreas, draining alka- line secretions and powerful enzymes through the major and minor papillae; and the stomach, producing caustic acids. It has a complex embryology involving develop- ment of adjacent organs and numerous anomalies. As a consequence of location, embryology, histology, surrounding structures and the adjacent organs draining into it, the pathology of the duodenum differs from that of other alimentary tract organs. Inch for inch and ounce for ounce, more distinct pathologies occur here than in any other abdominal organ.

Developmental phenomena give rise to annular pancreas, webs and choledochoceles, and account for ectopias.

Anatomy dictates patterns of obstruction and spread of disease from adjacent organs, as well as patterns of rupture Fig. 11. Submucosal, benign, spindle cell tumor of the gastric

antrum protruding into the lumen with a very smooth covering surface of stretched, but otherwise intact, surface epithelium

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and hematoma formation in blunt trauma. Exposure to gastric acid leads to ulcers and hyperplasias. Influx of bile and pancreatic juice is thought to determine some types and sites of mucosal neoplasia. The examples presented here will stress radiologic-pathologic correlation.

References

1. Theros E (1969) The value of radiologic-pathologic correlation in the education of the radiologist. AJR Am J Roentgenol 107:235-257

2. Lichtenstein JE (1986) (Revised 1991 and again revised by Gore R 1994) Basics of radiologic pathologic correlation in the GI tract. In: Tavaras JM, Ferrucci JT Jr (eds) Radiology:

diagnosis/imaging/intervention. Vol 4, Chp 4, Lippincott, Philadelphia, pp 1-19

3. Ladd AP, Madura JA (2001) Congenital duodenal anomalies in the adult. Arch Surg 136:576-584

4. Gore RM, Levine MS, Ghahremani GG, Miller FH (1970) Gastric cancer. Radiologic diagnosis. Radiol Clin North Am 35:311-329

5. Levine MS, Megibow AJ, Kochman ML (2000) Carcinoma of the stomach and duodenum. In: Gore RM, Levine MS (eds) Textbook of gastrointestinal radiology, 2nd ed. Saunders, Philadelphia, pp 601-626

6. Perez A, Saltzman JR, Carr-Locke DL et al (2003) Benign non- ampullary duodenal neoplasms. J Gastrointest Surg 7:536-541 7. Buck JL, Elsayed AM (1993) Ampullary tumors: radiologic-

pathologic correlation. Radiographics 13:193-212

8. Jean M, Dua K (2003) Tumors of the ampulla of Vater. Curr Gastroenterol Rep 5:171-175

9. Levy AD, Remotti HE, Thompson WM et al (2003) Gastrointestinal stromal tumors: radiologic features with pathologic correlation. Radiographics 23:283-304

10. Fletcher CD, Berman JJ, Corless C et al (2002) Diagnosis of gastrointestinal stromal tumors: a consensus approach. Hum Pathol 33:459-465

11. Miettinen M, El-Rafai W, Sobin LH, Lasota J (2002) Evaluation of malignancy and prognosis of gastrointestinal stromal tumors: a review. Hum Pathol 33: 478-483

12. Jayaraman MV, Mayo-Smith WW, Movson JS et al (2001) CT of the duodenum: an overlooked segment gets its due.

Radiographics Spec No:S147-S160

13. Lichtenstein JE, Scholz FJ (2005) Duodenum: basics of radiologic-pathologic correlations. In: Ros PR, Gourtsoyiannis NC (eds) Radiologic-pathologic correlation from head to toe.

Springer-Verlag, Berlin-Heidelberg, pp 253-272

14. Michelassi F, Erroi F, Dawson PJ et al (1989) Experience with 647 consecutive tumors of the duodenum, ampulla, head of the pancreas, and distal common bile duct. Ann Surg 210:544-554, discussion 554-556

15. Reeders JWAJ, Rosenbusch G (1994) Radiology of benign and malignant diseases of the duodenum. In: Freeny PC, Stevenson GW (eds) Margulis and Burhenne’s alimentary tract radiology.

Mosby, St. Louis, 467-511

16. Scholz FJ (1981) Duodenum in surgical radiology. In: Teplick JG, Haskin ME (eds) Surgical Radiology: A complement in radiology and imaging to the Sabiston Davis Christopher Textbook of Surgery. Saunders, Philadelphia, pp 502-537