Serendipitous actinomycosis infection mimicking malignant lesion in carcinoma of unknown primary

Abstract

Actinomycosis is a bacterial infection caused by Actinomyces species that are commensal in the human oral cavity, digestive tract, and genital tract. The present case highlights actinomycosis of the hypopharynx, mimicking malignancy in¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography.

Introduction

Actinomycosis is a bacterial infection caused by Actinomyces species, a type of filamentous, Gram-positive, nonacid-fast, anaerobic-to-microaerophilic bacteria, which are commensals in the human oral cavity, digestive tract, and genital tract.[1] Cervicofacial actinomycosis is the most common type (about 60%) followed by thoracic actinomycosis (15%–20%).[1]18 F-fluorodeoxyglucose (FDG) is a tracer widely used for imaging malignancy; however, it also localizes in the sites of infection and inflammation. Here, we describe a rare occurrence of FDG-positive actinomycotic lesion mimicking malignancy in a known case of carcinoma of unknown primary.

Case Report

A 50-year-old man presented with progressive bilateral neck swelling of 3 months. Biopsy from right level V node revealed metastatic squamous cell carcinoma. Whole-body FDG positron emission tomography-contrast enhanced computed tomography (PET-CECT) was done but could not detect a primary site of malignancy. The patient was treated with bilateral modified neck dissection, followed by adjuvant concurrent chemo-radiotherapy. Whole-body FDG PET-CECT was done 12 weeks after the completion of radiotherapy for response evaluation. It showed hypermetabolic soft-tissue thickening involving the right pyriform fossa (PFS) with maximum standard uptake value of 9.01 [Arrows in [Figure 1]a-c]. This appeared suspicious for a malignant etiology. Direct laryngoscopic examination revealed mucosal bulge in the right PFS. Subsequent histopathology revealed ulcerated squamous mucosa with necrosis and gram-positive actinomycotic colonies with abundant sulfur granules, with no evidence of malignancy [Figure 1]d, [Figure 1]e, [Figure 1]f, [Figure 1]g. The patient was put on anti-chondronecrosis treatment afterward.{Figure 1}

Discussion

Actinomycosis is a chronic granulomatous infection that can often present as a mass-like lesion and mimic malignancy.[2] With improving oral hygiene, the actinomycosis incidence is going down in developed countries, in developing countries; however, it still poses a problem.[3] Most of the literature on actinomycosis simulating malignancy are case reports of pulmonary actinomycosis.[4],[5],[6] Rarer still is literature describing FDG PET/CT findings of actinomycotic infection. We could find only two retrospective studies of small number of patients that tried to evaluate the role of FDG PET/CT in pulmonary actinomycosis. Their findings indicate that FDG PET/CT is of limited value in differentiating actinomycosis from malignancy.[2],[7] FDG concentrating actinomycosis of other organs can also easily be confused with malignant lesions as evidenced by the hand full of case reports published.[8],[9],[10] Actinomycosis of head and neck region mimicking malignant tumor has also been described in some case reports;[8],[9],[10] however, we could not find any case reports describing FDG PET CT findings of actinomycosis of the hypopharynx. Our case report is unique in that regard. In conclusion, such FDG-avid lesions pose quite a diagnostic challenge in a known or suspected case of malignancy and can easily confuse the clinician and should always be correlated with a proper histopathological and microbiological evaluation.

Declaration of patient consent

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Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.