Mycobacterium genavense infection of the adrenal gland - A case report

INTRODUCTION

Adrenal masses are frequently detected incidentally during abdominal and pelvic imaging performed for unrelated conditions. Evaluation requires a systematic approach to differentiate benign from malignant lesions, as this distinction directly affects management. Common etiologies include neoplasms such as adrenal adenoma, pheochromocytoma, metastases, as well as endocrine disorders such as Cushing syndrome. Adrenal infections, which can arise from fungi, viruses, parasites, or bacteria, are a less common cause of adrenal enlargement but should be considered alongside the differentials above.^[1] Infectious processes are often overlooked on initial radiologic differential diagnosis since they can mimic a neoplasm on imaging. Therefore, proper evaluation requires a combination of clinical history, imaging studies, laboratory tests, and histopathologic analysis.

CASE REPORT

A 48-year-old male presented to an outpatient clinic with complaints of leg swelling and tenderness. Ultrasound showed a thrombus in the common femoral vein, prompting further evaluation in the emergency department. Computed tomography (CT) venogram of the abdomen and pelvis confirmed thrombus in the external iliac, femoral, and deep femoral veins. This venogram also showed a previously unknown right adrenal mass measuring approximately 4 cm. Subsequently, a CT abdomen with and without contrast was obtained, showing a 3.8 × 3.0 cm right adrenal mass [Figures 1a-c].

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Figure 1:

A 48-year-old male presenting with a complaint of leg pain. Computed tomography abdomen showing a 3 cm right adrenal mass (arrow). (a) pre-contrast phase, (b) venous phase, (c) 15-minute delayed phase.

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Following the guidelines established in the evaluation of incidental adrenal masses,^[2] the lesion was characterized by its density measurement and contrast washout. Pre-contrast, venous, and 15-min delayed phase attenuation values were 39, 72, and 58 Hounsfield units (HU), respectively. Utilizing these values, the absolute percentage washout (APW) and relative percentage washout (RPW) were 42% and 19%, respectively. These findings excluded a cyst or hemorrhage, as these do not demonstrate enhancement (<10 HU). It also rules out a benign adenoma, which typically shows an APW of >60% or an RPW >40%. The lesion also failed to show an increased enhancement (>110–120 HU), which is characteristic of a pheochromocytoma. Given these indeterminate findings, further investigation with positron emission tomography–CT, biopsy, or surgical resection was recommended.

The patient had no known history of malignancy; however, the CT abdomen showed enlarged central mesenteric lymph nodes measuring up to 1.4 cm with additional prominent subcentimeter retroperitoneal nodes. These findings, in the setting of an indeterminate adrenal mass workup, raised concern for a neoplastic or infectious etiology, warranting resection and definitive tissue diagnosis. The patient was referred to surgery, where adrenalectomy was performed, with the specimen sent for pathology evaluation.

Gross examination of the specimen revealed an adrenal gland involved by an unencapsulated tumor with well-defined borders without areas of hemorrhage or necrosis. Histologically, the lesion was composed of sheets of epithelioid cells with abundant granular cytoplasm. Scattered non-necrotizing granulomas were also noted within the adjacent fibroadipose tissue [Figure 2a]. An immunohistochemical workup demonstrated that the epithelioid cells were positive for CD45 and CD68, consistent with macrophages. Immunohistochemistry for neoplastic markers SF1, calretinin, Cam5.2, Melan-A, synaptophysin, S-100, and chromogranin were all negative, ruling out adrenal cortical and medullary neoplasms as well as metastatic carcinoma. A Ki-67 proliferation marker was positive in <5% of epithelioid cells, indicating a lack of increased cellular proliferation typically associated with aggressive tumors. A workup for infectious causes included acid-fast bacillus (AFB) and Grocott’s Methenamine Silver (GMS) stains to evaluate for mycobacteria and fungi, respectively. AFB showed abundant intracytoplasmic bacilli [Figure 2b] with a negative GMS stain. Given these findings, the differential diagnosis included tuberculosis among other mycobacteria, such as Mycobacterium avium complex. To determine the specific infectious etiology, the specimen was sent for DNA sequencing. Polymerase chain reaction (PCR) testing for Mycobacterium tuberculosis complex was negative. Broad range bacterial PCR and sequencing confirmed the presence of Mycobacterium genavense.

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Figure 2:

A 48-year-old male after undergoing right adrenalectomy. Histology slide stained with (a) hematoxylin and eosin viewed at ×200 magnification showing a non-necrotizing granuloma (arrow). Histology slide stained with (b) acid-fast bacillus viewed at 600x magnification showing intracytoplasmic bacilli (arrow).

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The patient was referred to infectious disease and immunology specialists for management of this infection, as well as workup for possible immunodeficiencies that predisposed him to this condition. Human immunodeficiency virus (HIV) testing was negative, flow cytometry revealed low CD4+ and CD8+ T-cells, suggestive of an immunodeficiency such as CD4 lymphopenia, which may have increased his risk of M. genavense infection.

DISCUSSION

Granulomatous diseases are characterized by mass-forming aggregates of macrophages associated with chronic inflammation. They encompass a broad range of infectious and non-infectious etiologies, with disseminated granulomatous diseases most commonly caused by infection. In cases of M. tuberculosis and non-tuberculous mycobacterial infections, radiologic findings reflect the underlying granulomatous inflammatory processes identified on histopathologic examination.^[3] On histology, granulomas exhibit a variety of features, including a collection of macrophages, multinucleated giant cells, necrosis, and fibrosis. On imaging, this granulomatous inflammation may show a mass-like appearance with gland enlargement, central necrosis, fibrosis, calcifications, and enhancement after contrast injection.^[4] These findings, along with features such as lymphadenopathy, can overlap with those seen in malignancy, limiting the specificity of imaging and requiring histopathologic and molecular analysis for definitive diagnosis.

In this patient, PCR analysis revealed M. genavense, a rare pathogen primarily associated with disseminated infections in immunocompromised individuals, such as those with HIV/Acquired immunodeficiency syndrome^[5] or solid organ transplants.^[6] There are also reports of infection in non-HIV immunocompromised patients with an acquired immunodeficiency, such as idiopathic CD4 lymphopenia.^[7]Due to its rarity, no standardized treatment guidelines exist for the management of M. genavense infection, and therapy is often guided by expert recommendations and case reports. In general, management of M. genavense is similar to the regimen used for clinically similar Mycobacterium avium complex infections.^[8] In this case, identification of the infectious etiology for the adrenal mass prompted both antimicrobial treatment and evaluation for a possible underlying immunodeficiency.

CONCLUSION

This case presents a unique instance of an incidental finding leading to a rare diagnosis and emphasizes the importance of a comprehensive workup of such incidental findings. It highlights the use of advanced diagnostic modalities in identifying etiologies of diseases, including quantitative radiologic assessment, immunohistochemical staining, and molecular diagnostic techniques. Finally, this case shows the interdisciplinary collaboration between radiologists, pathologists, surgeons, and medicine specialists in the diagnosis and management of complex and atypical conditions to ensure optimal patient outcomes.