Salivary gland tumors account for less than 3% of head and neck tumors^[1]. Many case reports describes presence of more than one salivary gland tumor either synchronously or metachronusly^[2,3]. Several taxonomies are used to describe synchronous/metachronous occurrence of salivary gland neoplasms. Multiple salivary tumors may be considered from three standpoints: according to incidence time (synchronous or metachronous ), anatomical aspect (unilateral or bilateral), and histological aspect (identical or different pathology). Multiple malignant salivary tumors of identical pathology are much more common, which proposes the possibility of genetic risk factor, rather than only accidental event^[4]. Polymorphous  adenocarcinoma (PAC)  was first described in 1984, diagnoses is usually made based on the hematoxylin and eosin morphology. Solid nests of monotonous epithelial cells arranged in cribriform and trabecular masses. Focal papillary cystic areas can typically be present within the same lesion. The epithelial cells are usually cuboidal, columnar or spindle with eosinophilic cytoplasm. The nuclei are uniform, round or ovoid, with a characteristic “washed out” appearance. Mucous cells, clear cells or oncocytic cells may also be seen. The concentric whorling is noticed around regional neurovascular bundles “a targetoid appearance”, this perineural invasion (PNI) or neurotropism is a distinguishing feature of PAC and can be recognized in 30% of cases. While perineural involvement is common, mitotic figuresareuncommonandnecrosis is seeninhigh-grade transformation^[5].

PAC has a strong predilection to minor salivary glands of the palate. It tends to have lower local recurrence rates and lower metastatic potential however, PAC is invasive and locally destructive. Proper biopsy involving tumor periphery would help definitive identification of the tumor. Invasive growth at a lesion’s periphery, extension into non-neoplastic glands, perineural and lymphovascular invasions all are pathognomonic features of PAC. Immunohistochemistry is mandatory in absence of those diagnostic features. Long-term follow-up surveillance is necessary because recurrences have been reported to occur more than 10 years after initial treatment^[6]. Among all salivary gland tumors, pleomorphic adenoma (PA) is the most commonly encountered tumor, it accounts for about 60% of all salivary gland neoplasms. Parotid gland (superficial lobe) is the most common extra-oral site while palate is the most common intra-oral sit of PA. Pleomorphic adenoma presented clinically as rubbery painless mass with slow growth rate^[7]. Histologically, it is greatly variable in appearance hence the name pleomorphic adenoma. Characteristically it has a biphasic appearance, where a mixture of polygonal epithelial cells and spindle-shaped myoepithelial cells in a variable background stroma. Stroma could be cartilaginous, mucoid, myxoid or hyaline. Epithelial cells may be arranged in duct-like structures, sheets, clumps or interlacing cords. The tumor is not capsulated; however it is surrounded by a fibrous pseudocapsule of variable thickness^[8]. Surgical resection with adequate safety margin is the main treatment modality for salivary gland tumors. Underlying periosteal layer should be included with or without bone resection according to nature of the lesion. Radiotherapy is indicated as an adjuvant therapy if complete resection couldn’t be achieved, to improve local recurrence. Generally, irradiation is reserved for inoperable cases.

Co-occurrence of PAC and PA at the same time is very uncommon presentation with accidental detection during radiographic examination. Magnetic resonance imaging (MRI) superiority in detection of concealed soft tissue tumors is the key of diagnosis in such conditions. Perhaps adequate radiographic assessment for both minor and major salivary tissues is mandatory to avoid miss management of such cases. This work has been reported in line with SCARE 2018 ^[9].

A 52-year-old male patient visited the maxillofacial surgery outpatient clinic attached to AIN Shams University, complaining of palatal painless swelling over a period of two months. Past medical and surgical history was non-contributory. Social history was significant for 30 years of smoking. No significant family history was reported. Intra -oral clinical examination revealed 3x2x2.5cm rubbery well defined mass on the left side of the palate. Covering mucosa had normal looking with small surface ulceration 1x1cm (Figure 1). Intra-oral examination for other abnormalities was unremarkable. Clinical examination of related lymph nodes and other salivary glands fail to discover any positive finding. At this point minor salivary gland neoplasm was the preliminary diagnosis and our patient was scheduled for a diagnostic incisional biopsy. Meanwhile magnetic resonance imaging (MRI) examination of the head and neck was requested, the imaging showed 3x3x2cm heterogeneous soft tissue mass occupying the left maxilla crossing the midline with cortical impingement of underlying bone (Figure 2). Another well-defined homogenous circular mass 2x2 cm in superficial lobe of ipsilateral parotid gland was accidentally discovered, however no positive lymph nodes detected (Figure 3).

Incisional biopsy under local anesthesia was done for diagnosis of palatal swelling. Pathology report diagnose the palatal tumor as “polymorphous  adenocarcinoma (PAC). Ultra sound (US) guided fine-needle aspiration cytology (FNAC) of parotid mass was done showing a histopathological picture suggestive of pleomorphic adenoma (Figure 4). Work up was done to exclude other primary or synchronous tumors including chest computed tomography (CT) and abdominal ultrasound.

The decision was made to surgically resect the palatal tumor with one centimeter safety margin including the underlying palatine bone and insertion of immediate obturator (Figure 5). For synchronously discovered parotid tumor superficial parotidectomy with facial nerve preservation was done through modified Blair incision followed by primary closure (Figure 6). Operative time was five hours with blood loss about 250-350mm, no intra or post-operative complications were recorded. Patient was discharged two days after operation. Treatment plane was explained to the patient to ensure his acceptance before obtaining informed consent. Resected palatal mass showed perineural invasion (as testified by pathology report) accordingly the patient was scheduled for postoperative radiotherapy to control perineural invasion of greater palatine nerve. External beam radiation 60Gy five days per week for six weeks was the recommended protocol by radiotherapist. Patient was free from recurrence after follow up for one year with intact facial nerve function. Two weeks after first radiation dose the patient complains of xerostomia, sore throat, burning mouth, hoarseness, dysphagia, pain, and marked limitation in mouth opening. However, these side effects diminished after two months except for xerostomia.

Although salivary gland neoplasms remain idiopathic, there are many risk factors reported in literature including radiation, genetic predilection, excessive smoking, certain oncogenic viral infections and exposure to certain chemicals. Excessive exposure to diagnostic or therapeutic radiation has considerable increased risk of salivary gland neoplasia. There is also significant risk for carcinoma of other organs secondary to primary benign or malignant salivary tumors, especially breast, thyroid, bronchus and ovary^[10-12]. Polymorphous  adenocarcinoma (PAC) were the most reported minor salivary tumor in cases of multiple salivary neoplasms. The mean age for patients with multiple malignant salivary gland neoplasms at the time of their first primary tumor was 53 years^[13]. Both findings are consistent with our case report.

In cases of multiple salivary tumors pathology of each lesion should be addressed separately. If histopathology is similar the possibility of there being one primary tumor with distant metastasis should be considered^[3]. In case of different pathology each tumor should be treated independently according to location, size, anatomical extension as well as histological phenotype^[4]. Recently PAC has been differentiated from a new pathologic variant of salivary tumor named mammary analog secretory carcinoma (MASC). The present case showed clear microscopic features of PAC, in addition there is no conclusive evidence that (MASC) should be treated differently than any other low-grade malignant salivary gland tumors, though high-grade transformation has been described^[14].

Radiological examination is mandatory in salivary tumors workup. Although ultra sound US is useful in imaging of superficial masses it neither detects malignant features nor invasion of surrounding tissues^[13]. The next step in diagnosis is biopsy; FNAC is most commonly adopted technique for diagnosis of parotid tumors. It is a quick and safe sampling technique that can be performed readily in the outpatient setting with high specificity and diagnostic accuracy (89% and 85%). However it is technique sensitive. Sensitivity for detecting malignancy has been reported between 70% and 80%. The diagnostic accuracy can be increased significantly when used in conjunction with a cytology and Image guidance. In the present case US was used to guide fine needle aspiration cytology (FNAC) to overcome sampling error^[15,16]. CT with contrast is the most commonly used investigation in diagnosis of salivary tumors. In fact MRI is superior in early detection of soft tissue changes and characterization of malignant nodal involvement, detection of underlying bone marrow infiltration as well as anticipation of perineural spread^[17]. Lymph node involvement in MRI is specified by two criteria: size larger than one centimeter with loss of central fat (central necrosis). The use of MRI rather CT in the present case allows clear detection of coincident parotid lesion that could be missed by CT. None of the examined lymph-nodes showed such criteria accordingly we adopt wait and see policy with frequent clinical and radiographic follow-ups^[18,19].

In the present case both lesions were surgically managed in the same operation. Minor salivary tumor PAC was resected with one cm safety margin including underlying palatal bone to ensure tumor free margins as recommended by literature^[13]. Insertion of immediate opturator after resection of PAC was decided since it allows frequent examination of the surgical bed for detection of tumor recurrence. Superficial parotidectomy with facial nerve dissection and preservation was the treatment of choice for benign PA^[6]. It has been reported in literature that simple enucleation of PA is associated with high recurrence rates (8% and 45%), which is reduced to less than 5% with superficial parotidectomy and 0.4% with total parotidectomy. this was attributed to presence of microscopic extensions protruding beyond pseudocapsule or by capsular penetration^[20,21]. Unfortunately histopathological evidence of perineural invasion of PAC (through greater palatine nerve) mandate radiation therapy which adds to patient disability. Kämmerer et al, in 2009 report a case of polymorphous lowgrade adenocarcinoma misdiagnosed by incisional biopsy as PA, excisional biopsy later on revealed areas of small malignant fractions of the specimen besides a major part of benign tissue formations. Our case could be a logic explanation of such contribution. Where palatal tumor started as PA and transformed gradually into PAC. By this explanation both tumor would have same pathology at initial presentation^[22]. We aim to report a rare incidence of multiple primary synchronous salivary tumors of different pathology. Where, the use MRI in diagnosis of salivary tumors is mandatory to detect even early small coincident salivary tissue involvements.

The use of MRI examination is mandatory for exclusion of multiple salivary tissue involvement especially if patient has risk factors for malignancy (e.g.: smoking, old age).

Ethical approval has been exempted by faculty ethical committee based on absence of any risk or violation of applied guidelines in such cases.

All authors declared that there are no conflicts of interest.

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