Post-operative Diagnosis of Primary Parotid Tuberculosis in a Patient Initially Diagnosed as Benign Pleomorphic Adenoma

Abstract

Primary parotid tuberculosis is a well-known but extremely rare entity even in endemic countries. Most of the cases are diagnosed late in the course of illness when the parotid shows features of cold abscess leading to facial disfigurement. Early diagnosis is a clinical challenge due to lack of clinical suspicion as well as absence of clinical or radiological tests suggestive of the disease. Fine needle aspiration cytology features of early tuberculosis can easily be confused with a pleomorphic adenoma. When ultrasound examination of a parotid lesion is atypical, image guided core needle biopsy can be helpful in differentiating these kinds of rare diseases from more common parotid pathologies.

Introduction

Tuberculosis is endemic in many Asian and African countries. Extrapulmonary tuberculosis, which affects virtually any organ, makes a heavy load in these countries yet salivary gland tuberculosis is only rarely reported [1]. Primary salivary involvement can be due to direct spread from oral cavity through the ducts and inhibitory effect of continuous flow of saliva as well as presence of thiocyanates/lysozyme in the salivary secretion has been attributed as the reason for rarity [2]. Secondary spread is through hematogenous route, either the gland or intraglandular/ adjacent lymph node deposition extension leading to a parotid abscess [1, 2]. We present a case of primary parotid tuberculosis which was diagnosed post operatively, the surgery done for a pleomorphic adenoma.

Case Presentation

A 55-year old female patient without any known co-morbidities presented with a painless swelling in front of the right ear of 2-month duration. The size remained static and there were no features of local inflammation. Any history of fever, cough, loss of appetite or loss of weight was absent. There was no past or family history of tuberculosis. Local examination revealed a 1 × 1 cm non-tender round firm swelling with smooth surface clinically confined to the superficial lobe of the parotid gland. Facial nerve examination was normal. Cervical lymph nodes were not palpable on either side. Oral hygiene was good and parotid duct opening apparently normal. Examination of the tonsils to exclude a deep lobe tumor was normal. Total and differential count, ESR and other pre anesthetic blood tests were normal. Ultrasonography of the parotid gland and neck revealed 1 × 1 cm well defined mixed echo texture lesion confined to the superficial lobe of the parotid gland (Fig. 1a) with no cervical lymphadenopathy. Fine needle aspiration cytology (FNAC) result showed features suggestive of benign pleomorphic adenoma (loose clusters of spindle cells, a few epithelial cells and plasmacytoid-(myoepithelial)-cells with abundant pale cytoplasm. Also seen few multi nucleated giant cells. Background showed scant fibro myxoid material) as shown in the pathology slides (Fig. 2). Patient underwent superficial parotidectomy with preservation of all the branches of facial nerve under general anesthesia without cutting in to the tumour and the plane of resection has been unremarkable. She was discharged on the first post-operative day with no wound related complications. Gross specimen examination showed a well-defined lesion in the superficial lobe of the parotid gland (Fig. 1b). Histopathological examination of the specimen reported caseating granulomatous inflammation consistent with tuberculosis of the parotid gland (macroscopic finding: 2 × 2 × 1.3 cm sized tan coloured well defined growth. Microscopic finding: normal salivary acini showing well-formed granulomas composed of epithelioid histiocytes, Langerhans giant cells, multi nucleated foreign body type giant cells, foci of caseation necrosis, fibroblasts and collections of lymphocytes). Patient came for follow-up on the seventh post-operative day with a 10 ml asymptomatic wound seroma, which was aspirated and send for GeneXpert®. Chest X-ray, Mantoux test, and sputum for AFB was also done. All the investigations including GeneXpert® were negative for tuberculosis. Based on the histopathological finding she was diagnosed with primary tuberculosis of the parotid gland confined to the superficial lobe and was treated with anti-tuberculous therapy under the DOTS regimen for six months (2 months of Isoniazid, Rifampicin, Ethambutol and Pyrazinamide followed by 4 months of Isoniazid and Rifampicin) She has been asymptomatic after 10 months of surgery on follow up with a good cosmetic healed scar of parotidectomy incision.

Fig. 1.

a Well defined mixed echotexture lesion in superficial parotid gland, ultrasound scan. b Specimen photograph of well circumscribed lesion in parotid gland

Fig. 2.

Histology picture of tuberculosis parotid gland

Discussion

Fifteen to twenty percent of tuberculosis affects extra pulmonary organs of which salivary gland is a rare site. [3] Parotid is the most common among the salivary glands where a slow growing painless swelling mimicking a tumor can occur early in the phase of the disease. This poses a diagnostic challenge as opposed to the classical presentation of overt disease with redness, trismus, skin adhesions, cold abscess and multiple discharging sinuses [4, 5]. Early diagnosis is of paramount importance to avoid a disfiguring scar on the face, but short duration of the swelling, slow but gradual progression and some discomfort in the region are the only clinically relevant clues available to the physician. Moreover, there are no clinical, radiological, or biological criteria to make a definitive diagnosis. Even though some cases reported in the literature were diagnosed only with ultrasonography (USG) and fine needle aspiration cytology (FNAC), a few of them required surgical procedure (superficial parotidectomy) and histopathological examination for a definitive diagnosis [2].

High frequency ultrasonogram (USG) is sufficient as a preoperative imaging in small lesions with benign cytology if the lesion is confined to the superficial lobes [4]. Though USG is not specific to tuberculosis, a hypo echoic lesion with minimal delineation with the surrounding tissues can raise the suspicion of not being a tumor [5] CT or MRI are mandatory in large lesions and obviously will contribute to clinical suspicion of an inflammatory pathology [6, 7]. However, the use of USG alone as a preoperative imaging constitutes a limitation in our study.

Cutting into a parotid for an open biopsy is contraindicated due to the risk of tumor rupture, facial nerve injury and difficult dissection in a future surgery. FNAC is the routine preoperative tissue diagnostic tool in a parotid swelling and it is often sufficient in most of the pathologies [8]. Cytology of the early tuberculosis can easily be confused with a pleomorphic adenoma. There is a confusing similarity between epithelioid histocytes and bland spindle cells of tuberculosis with myoepithelial cells having epithelioid shape and mesenchymal cells respectively of a pleomorphic adenoma [9]. Multinucleated giant cells typical of tuberculosis can be seen in pleomorphic adenomas as well [9]. Of late, ultrasound guided core needle biopsy is being increasingly used in parotid lump evaluation and it is likely to help in the process of diagnosing parotid pathologies including tuberculosis to a greater extent even when the clinical and radiological clues are not evident [10].

Funding

No financial disclosure.

Compliance with Ethical Standards

Conflict of interest

No conflicts of interest.