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Original Report |
1 Department of Radiology, National Naval Medical Center, 8901 Wisconsin Ave.,
Bethesda, MD 20889-5600.
2 Department of Radiology and Nuclear Medicine, Uniformed Services University of
the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814.
3 Department of Radiologic Pathology, Armed Forces Institute of Pathology, 14th
St. and Alaska Ave., N.W., Washington, DC 20306-6000.
4 Present address: Department of Radiology (RR215), University of Washington,
1959 N.E. Pacific, Box 357115, Seattle, WA 98195-7115.
5 Department of Hematopathology, Armed Forces Institute of Pathology,
Washington, DC 20306-6000.
6 Department of Gastrointestinal Pathology, Armed Forces Institute of Pathology,
Washington, DC 20306-6000.
Received September 17, 2001;
accepted after revision October 24, 2001.
The opinions and assertions contained herein are the private views of the
authors and are not to be construed as official or as reflecting the views of
the Departments of the Navy, Army, Air Force, or Defense.
Abstract
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CONCLUSION. Non-Hodgkin's lymphoma of the appendix typically manifests with acute symptoms in patients who have no prior history of lymphoma. Most patients with the disease present clinically with signs and symptoms suggestive of acute appendicitis. On CT, lymphomatous infiltration of the appendix produces markedly diffuse mural soft-tissue thickening (range of diameters, 2.5-4.0 cm; mean diameter, 3.2 cm). The vermiform morphology of the appendix is usually maintained, and aneurysmal dilatation of the lumen is sometimes seen. Stranding of the periappendiceal fat seen on CT may represent superimposed inflammation or even direct lymphomatous extension. Coexisting abdominal lymphadenopathy is not seen in all patients. Although appendiceal lymphoma is rare, the characteristic CT appearance could lead to a preoperative diagnosis.
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Operative reports, surgical pathology reports, and photographs of the resected gross specimens for all five patients were available for review and were directly correlated with the CT findings. H and E—stained slides were available for review for five patients, and immunohistochemically stained slides were available for review for four. The slides in each case were reviewed by a gastrointestinal pathologist and hematopathologist. The lymphomas were categorized according to the revised European—American classification of lymphoid neoplasms of the World Health Organization (WHO) classification of tumors [3].
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On CT, marked homogeneous enlargement of the appendix with relative preservation of the vermiform morphology was seen in all five patients (Figs. 1A,1B,1C,1D,2A,2B,2C,3A,3B,3C,3D). The maximal appendiceal diameter ranged from 2.5 to 4.0 cm (mean diameter, 3.2 cm). The maximal diameter was 3.0 cm or larger in four of the five cases. In patients in whom the lumen could be identified on CT, the wall thickening appeared circumferential and measured more than 1 cm (Fig. 1A,1B,1C,1D). None of CT scans of the patients showed cystic luminal dilatation that would suggest mucocele formation. However, a mild tubular expansion of the lumen similar to the aneurysmal dilatation seen in small-bowel lymphoma was apparent on imaging and pathologic examinations in the two patients without appendicitis (Fig. 1A,1B,1C,1D). In the three patients in whom lymphoma presented as appendicitis, soft-tissue infiltration of the periappendiceal fat was found and graded as mild in one case and moderate in the two other cases (Figs. 2A,2B,2C and 3A,3B,3C,3D). No evidence of mural thickening or intraluminal mass suggestive of involvement of other gastrointestinal sites was seen in the stomach, small bowel, or colon. The solid abdominal organs were normal. In three patients, mild but measurably discrete abdominal lymphadenopathy (>1 cm in the short axis) was located in the retroperitoneum (in two patients) or in the mesentery (in one patient).
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The original preoperative CT interpretations for four patients were available for review. The possibility of an appendiceal neoplasm was not raised in any of these reports. The massively enlarged appendix was not recognized as such in any of the four patients but rather was interpreted to most likely represent a phlegmon or abscess in three patients and an extraintestinal nodal mass in the fourth. Similarly, the aneurysmal appendiceal lumen that was opacified on the barium examination in one patient was interpreted as probably originating in the small bowel (Fig. 1A,1B,1C,1D).
At pathologic examination, the appendix in all five patients was found to be grossly enlarged with diffuse tannish wall thickening (Figs. 1A,1B,1C,1D,2A,2B,2C,3A,3B,3C,3D). Appendiceal diameter ranged from 2.5 to 4.5 cm (average diameter, 3.8 cm), and appendiceal length ranged from 7 to 17 cm (average length, 11.9 cm). Gross appendiceal morphology consisting of vermiform enlargement correlated well with the CT appearance. Diffuse lymphocytic infiltration of the appendiceal wall was identified in each patient (Fig. 3A,3B,3C,3D). Periappendiceal inflammation or necrosis was seen in the three patients with lymphoma presenting as appendicitis. However, lymphomatous extension into the periappendiceal fat was also documented in one of these patients as well as in the patient who presented with gastrointestinal bleeding. Clinical presentation in one patient was believed to be related to torsion of the enlarged appendix at surgery (Fig. 1A,1B,1C,1D).
The tumors were classified as mantle cell lymphoma in two patients, diffuse large B-cell lymphoma in one patient, non-Hodgkin's lymphoma consistent with diffuse large B-cell lymphoma in one patient, and large cell undifferentiated malignancy consistent with diffuse large B-cell lymphoma in one patient. In one of the two mantle cell cases, pathologic examination revealed lymphoma in the appendix and terminal ileum (lymphomatous polyposis). In the remaining four patients, pathologic examination was limited to the appendix.
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Information on appendiceal lymphoma is mainly limited to scattered case reports and letters in the clinical and pathology literature [5,6,7,8,9], with even fewer case reports focusing on the imaging features of the disease [10, 11]. Involvement of the appendix is inconsistently reported in larger series of gastrointestinal tract lymphoma, but the frequency of such involvement appears to range from 1% to 3% [4, 5]. The demographic profile for patients with appendiceal lymphoma in our series was similar to that cited earlier for other gastrointestinal tract lymphomas. To our knowledge, all reported cases of appendiceal lymphoma have been of the non-Hodgkin's variety.
When considered collectively, our patients share many common features with previously reported cases of appendiceal lymphoma. Most patients presented with acute symptoms of appendicitis or, less frequently, with lower gastrointestinal bleeding. Most of the cases represented primary disease, although recurrence manifesting as appendiceal involvement has been reported and was seen in one of our patients [9]. Diffuse enlargement of the appendix from lymphomatous infiltration was noted in essentially all patients with a pathology report. For the previously reported cases [5,6,7,8,9], the average appendiceal diameter at pathologic examination was approximately 3 cm, which is similar to our findings.
Diffuse appendiceal enlargement on CT is generally regarded as a sign of appendicitis, especially if the finding is associated with stranding of the periappendiceal fat in a patient with acute right lower quadrant abdominal pain. A diameter of 6-7 mm is well established as the diagnostic threshold for appendicitis on both sonography and CT [12]. What is lacking, however, is sufficient data on an upper-limit diameter, above which one should consider infiltrative neoplasms in addition to standard, nontumoral appendicitis. Because the inflamed appendix without neoplasm will usually not exceed 15 mm in diameter on CT [12], enlargement beyond this size should be viewed with suspicion. Even more concerning is an appendiceal diameter measuring 2.5 cm or more, as seen in all five patients in our series. A clinical presentation of appendicitis and periappendiceal stranding on CT does not militate against the possibility of an offending neoplasm in such patients.
Several other observations from our study warrant brief consideration. One apparent pitfall in the CT diagnosis of appendiceal lymphoma is misinterpreting the grossly abnormal appendix as a thickened small-bowel loop or an extraintestinal process, such as a nodal mass, phlegmon, abscess, or (in women) adnexal disease. Recognizing both the relationship of the appendix to the cecum and the blind-ended structure of the appendix is crucial for proper diagnosis. In reviewing the pathologic findings in our study, we found that the presence of periappendiceal stranding visible on CT can be due either to inflammatory changes from secondary appendicitis or to direct serosal extension of lymphomatous cells. The aneurysmal dilatation of the appendiceal lumen seen in our patients who did not have appendicitis appeared to be similar to observations in patients with small-bowel lymphoma. Aneurysmal dilatation in those patients was believed to have resulted from lymphomatous replacement of the muscularis propria and destruction of the autonomic nerve plexus [2]. To our knowledge, this finding in the appendix has not been described previously. Last of all, the diagnosis of gastrointestinal tract lymphoma is particularly relevant in patients with immunocompromise, including patients with AIDS and solid-organ transplant recipients. In these patient populations, extranodal disease accounts for more than 80% of abdominal lymphoma detected on CT [13, 14].
Although the CT finding of prominent vermiform soft-tissue enlargement of the appendix seems to be fairly characteristic of non-Hodgkin's lymphoma, such a finding is not pathognomonic. Neuroendocrine tumors represent another group of primary appendiceal neoplasms that can show an infiltrative pattern of growth. Specific examples include the carcinoid tumors (classical, goblet cell, and tubular subtypes), paraganglioma, and ganglioneuroma [15, 16]. However, the most common tumor in this group, the classical carcinoid, usually forms a focal subcentimeter mass in the distal third of the appendix that is quite distinct from the appearance of circumferential infiltration [17]. The remaining neuroendocrine tumors are rare but may occasionally show prominent vermiform enlargement of the appendix that would appear similar to the appearance of lymphoma on CT [18]. The more common mucinous epithelial neoplasms of the appendix will generally form mucoceles that reveal obvious cystic dilatation of the lumen on CT, with or without mural calcification [15, 19].
Among the limitations to our study is the fact that because appendiceal lymphoma is rare, our patients were referred over a period of many years, and therefore, CT techniques used to obtain the scans varied, making assessment of enhancement patterns difficult. Furthermore, although the morphologic appearance of the lymphomatous appendix was consistent in our series, the small number of patients precludes definitive conclusions. However, our findings are supported by the similar descriptions that appear in previous case reports [5,6,7,8,9].
In conclusion, non-Hodgkin's lymphoma of the appendix in our series revealed a striking soft-tissue enlargement on CT with relative maintenance of the vermiform morphology. On CT, the diameter of the lymphomatous appendix usually measures 3 cm or larger, which is out of proportion to the size expected for nontumoral appendicitis and should allow one to make a presumptive diagnosis of appendiceal neoplasm. Although the CT appearance is not pathognomonic and can be seen occasionally with other primary appendiceal neoplasms, non-Hodgkin's lymphoma should be the lead differential diagnosis. Specificity for lymphoma will be increased in the setting of abdominal lymphadenopathy or aneurysmal dilatation of the appendiceal lumen.
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