Renal actinomycosis mimicking renal tumor: case report.

Abstract: A 68-year-old man was admitted after fever and general fatigue with severe inflammatory signs and anemia. T1- and T2-weighted magnetic resonance imaging showed low- to isointensity and low-intensity tumor in the right kidney, respectively, suggesting renal actinomycosis. However, the right kidney was explored transabdominally because the possibility of renal malignant lymphoma could not be excluded. After nephrectomy, characteristic colonies of Actinomyces were seen microscopically, and the histologic diagnosis was renal actinomycosis. The patient was treated with antibiotics and made good progress after operation. This case highlights the importance of magnetic resonance imaging for the diagnosis of renal actinomycosis.

Key Words: actinomycosis, kidney, magnetic resonance imaging

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Actinomycosis is a chronic systemic fungal infection caused by Actinomyces israelii and related anaerobic filament. A. israelii is usually nonpathogenic; however, it makes granuloma as actinomycosis when the host defense is disrupted. Since the first case of solitary renal actinomycosis was described in 1878, (1) this condition has been reported sporadically. We report a case for which the diagnosis was renal actinomycosis after nephrectomy. In addition, this report presents radiographic characteristics of renal actinomycosis according to the literature.

Case Report

A 68-year-old man presented with a 10-year history of hypertension and anxious neurosis. Two months before admission, common cold-like symptoms such as general fatigue and fever were seen. He was admitted to our hospital after an episode of severe inflammatory signs and anemia in February 1997.

On physical examination, his blood pressure was 150/50 mm Hg and his pulse rate was 88 beats/min and regular. His body temperature was 38.6[degrees]C. Anemia was observed in his conjunctiva; however, goiter was not palpable, and heart, lung, and abdomen were normal. Neurologic examinations revealed no other abnormalities.

Regarding laboratory data at admission, the urinary examination showed proteinuria and hematuria. The erythrocyte sedimentation rate was 138 mm/h. Hematologic data showed severe anemia (hemoglobin, 7.9 g/dl), leukocytosis (white blood cell count, 13,600/[micro]l), and thrombocytosis (platelet count, 77.8 X [10.sup.4]/[micro]l). Serum aminotransferase levels were normal (aspartate aminotransferase, 27 IU/L; alanine aminotransferase, 34 IU/L). Serum cholinesterase level was decreased (2,109 IU/L; normal range, 3,500-8,000 IU/L) and C-reactive protein was 18.4 mg/dl (normal range, <0.6 mg/dl). Serum creatinine was 1.3 mg/dl and uric acid was 3.9 mg/dl. Fasting plasma glucose was 128 mg/dl and hemoglobin A1C was 5.6%. Antinuclear antibody and tumor markers were within normal ranges. Urinary and blood cultures including Gram's stain were all negative. Cytology of urine was Class II.

Ultrasonography revealed a low echoic solid mass of the right upper to middle kidney. Abdominal enhanced computed tomographic (CT) scan showed an enlarged right kidney (13 X 8 X 10 cm) and the poorly enhanced mass by using contrast medium (Fig. 1).

After piperacillin sodium administration for general inflammation, the size of the renal tumor was slightly decreased; however, inflammatory signs were not improved. The patient was transferred to the surgical unit of another hospital. Gallium [.sup.67]Ga scintigraphy revealed strong accumulation in the right kidney. In addition, an avascular region was observed in the right upper kidney by right renal angiography. T1-and T2-weighted magnetic resonance imaging (MRI) showed low-to isointensity and low-intensity tumor, respectively (Fig. 2). On the basis of these examinations, renal actinomycosis was suspected; however, final diagnosis could not be made before operation. Renal cell carcinoma and renal abscess were denied in the present case, because renal cell carcinoma is usually indicated as a hypervascular mass with vascular abnormalities on angiography, and renal abscess is characterized as an unenhanced mass with dense contrast enhancement in the walls on enhanced CT scan and high-intensity lesion on T2-weighted MRI. The right kidney was explored transabdominally because the possibility of renal malignant lymphoma could not be excluded. Macroscopically, a whitish-yellowish nodular mass that was adhesive to adjacent tissues was found in the right upper kidney. The cut surface showed multiple nodules below 2 cm, with unclear margins (Fig. 3, left). Microscopic study revealed an inflammatory mass with lymphocytes, plasma cells, and fibroblast infiltration (Fig. 3, right). These masses were scattered multifocally in the kidney. Characteristic colonies of Actinomyces stained by hematoxylin in the center and by eosin in the peripheral region were seen. These pathologic findings were consistent with actinomycosis.

Discussion

The organism causing actinomycosis is known to exist as an anaerobic, harmless saprophyte in the mouth, tonsils, and gastrointestinal tract. (1) The clinical types of actinomycosis are cervicofacial in 60%, thoracic in 15%, and abdominal in 25% of cases. (2) It was reported that the appendix is the most common organ affected by abdominal actinomycosis. (3) Renal actinomycosis is relatively rare. Since the first case of solitary renal actinomycosis was described in 1878, (1) only approximately 50 cases have been described. (4)

The routes of infection to the kidney include the bloodstream and direct expansion from contiguous structure, (1) although infection before actinomycosis in the present case could not be determined. The patient had untreated dental caries, which caused repeated oral infection, suggesting that A. israelii and/or related anaerobic filaments in the oral cavity could have been the source of the infection in the kidney.

Actinomyces are seldom found in the urine, (1) although pus cells may be plentiful and secondary infection may be present. The definite diagnosis is generally based on histologic identification with colonies of Actinomyces. (5) In the present case, histologic study revealed colonies of Actinomyces.

[FIGURE 1 OMITTED]

A number of authors emphasize the difficulties involved in arriving at a diagnosis preoperatively. (1,5) Early diagnosis is important for minimizing the morbidity of disease and preventing unnecessary surgery. However, radiologic findings are usually nonspecific. The findings of an avascular or hypovascular mass on angiography and accumulation of [.sup.67]Ga on scintigraphy are still not helpful for making the definite diagnosis of actinomycosis. (6) Radiologically, a vascular mass including renal leiomyoma, renal pseudotumor caused by pyelonephritis, and papillary renal adenocarcinoma should be differentiated. (7)

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

CT scanning is useful for showing the extent and characteristics of abdominal actinomycosis. It was reported that dense contrast enhancement in the walls or solid components of the masses was noted in 80% of patients, (6) although these appearances are nonspecific in actinomycosis and sometimes can be seen in other inflammatory diseases.

MRI could be a most useful tool for diagnosis of renal actinomycosis. Actinomycosis is characterized as a low- to isointensity mass on T1-weighted MRI and as a low-intensity mass on T2-weighted MRI. The finding of a low-intensity mass on T2-weighted MRI should particularly be emphasized because most cases with actinomycosis show this feature. (8) MRI findings in the present case showed the same characteristics as above.

Actinomycosis has sometimes been misdiagnosed as another neoplasm, (1,2,4,5) especially as malignant lymphoma, and nephrectomy has been performed to establish the diagnosis. However, renal malignant lymphoma is characterized on MRI as an iso- to high-intensity mass on T2-weighted MRI, which is different from the finding of actinomycosis.

Renal actinomycosis is a rare granulomatous disease; however, its diagnosis is rarely anticipated preoperatively, Careful observations and detailed examinations including MRI are necessary for the diagnosis.

Conclusion

We report the case of a 68-year-old man with renal actinomycosis. T1-and T2-weighted MRI showed low-to isointensity and low-intensity tumor in the right kidney, respectively, suggesting renal actinomycosis. However, because the possibility of renal malignant lymphoma could not be excluded, the right kidney was explored transabdominally. Microscopically, characteristic colonies of Actinomyces were seen and the histologic diagnosis was renal actinomycosis.

Accepted January 30, 2003.

Copyright [c] 2004 by The Southern Medical Association

0038-4348/04/9703-0316

References

1. Patel BJ, Moskowitz H, Hashmat A. Unilateral renal actinomycosis. Urology 1983;21:172-174.

2. Khalaff H, Srigley JR, Klotz LH. Recognition of renal actinomycosis: Nephrectomy can be avoided--Report of a case. Can J Surg 1995;38:77-79.

3. Allen HA III, Scatarige JC, Kim MH. Actinomycosis: CT findings in six patients. AJR Am J Roentgenol 1987;149:1255-1258.

4. Crosse JE, Soderdahl DW, Schamber DT. Renal actinomycosis. Urology 1976;7:309-311.

5. Morgan RJ, Molland EA, Blandy JP. Renal actinomycosis. Eur Urol 1977;3:307-308.

6. Ha HK, Lee HJ, Kim H, et al. Abdominal actinomycosis: CT findings in 10 patients. AJR Am J Roentgenol 1993;161:791-794.

7. Nakajima H, Yui Y, Tsuboi N, et al. A case of renal cell carcinoma difficult to diagnose preoperatively because of hypovascular findings [in Japanese]. Hinyokika Kiyo 1985;31:1021-1025.

8. Hawnaur JM, Reynolds K, McGettigan C. Magnetic resonance imaging of actinomycosis presenting as pelvic malignancy. Br J Radiol 1999;72:1006-1011.

RELATED ARTICLE: Key Points

* We report the case of a patient diagnosed with renal actinomycosis after renal exclusion.

* It was difficult to distinguish renal actinomycosis from malignant lymphoma before operation.

* Retrospectively, magnetic resonance imaging could be useful for the diagnosis of the renal actinomycosis.

Taro Horino, MD, Michiya Yamamoto, MD, PHD, Masaru Morita, MD, Toshihiro Takao, MD, PHD, Yukio Yamamoto, MD, and Takamaro Geshi, MD, PHD

From the Departments of Internal Medicine and Psychiatry, Geshi Hospital, Kochi, Japan; the Departments of Radiology and Urology, Chikamori Hospital, Kochi, Japan; and the Second Department of Internal Medicine, Kochi Medical School, Nankoku, Japan.

Reprint requests to Taro Horino, MD, Second Department of Internal Medicine, Kochi Medical School, Kohasu, Okoh-cho, Nankoku, Kochi 783-8505, Japan. Email: [e-mail]