FINAL DIAGNOSIS
Epithelial-Myoepithelial Cell Carcinoma (EMCC)
TREATMENT AND FOLLOW UP
Intensity Modulated Particle radiotherapy (IMPT) with carbon ions was planned. A total dose of 68.8 Gy over 16 fractions was administered focusing on the right pterygopalatine fossa and extending cranially to the clivus region. After radiotherapy the patient reported as treatment sequelae a right palpebral edema and a mucositis of the inner right cheek. A maxillary MRI with Gd showed a consistent reduction of the neoplasm volume (Figs. 2a, 2b). The efficacy of the therapy was confirmed by an 18-FDG PET) performed two months later. Clinically, the patient showed an almost complete improvement of the right eye ptosis and lateral gaze diplopia with the persistence only of the right V2 hypoesthesia.
DISCUSSION
To our knowledge, we reported the first case of EMCC arising in Meckel's cave. EMCC is a rare malignancy comprising 1% of all salivary gland tumors that was firstly described by Donath et al. in 1972 (1). EMCC mainly affects female patients (1,5 :1) ranging in age from the third to the eight decade of life (2). The mean age at onset is 60.9 years (2,3).
According to the World Health Organization (WHO) classification of salivary glands tumors, EMCC is characterized by the simultaneous presence of two different cell types in varying proportion (4). The histological hallmark of this tumor is the bi-layered epithelial-myoepithelial phenotype. The tumor is composed of dark cells nets arranged in tubules similar to those of the intercalated ducts. These cells are positive for epithelial markers (cytokeratins and epithelial membrane antigen) but negative for myoepithelial markers (alpha-smooth muscle actin, P63, vimentin). By contrast, the outer layer is composed of light cells positive for myoepithelial markers (5). This dual differentiation can be explained with the presence of a common precursor of the two tumor components (3).
EMCC usually shows low malignancy and is associated with a favorable prognosis. Despite its low-grade malignant nature, perineural infiltration is usually seen in these tumors (6). According to most Authors the recurrence rate varies from 35 to 50% with a low metastatic risk (from 8 to 25%) (7,8,9). The 5 and 10 year disease survival rates are 93.5 and 81.8% respectively (7,8).
EMCC generally arises from the parotid gland (from most series 62.1% - 83.74%) and less commonly from submandibular gland (8,6%) or from other minor salivary glands (8,6%) (8,9,10,11). It can rarely arise from the lacrimal gland (12) or sinonasal mucoserous glands (< 10%) (13).
In addition, the presence of salivary gland tissue apart from major or minor salivary glands (heterotropia) has been reported in various districts of head and neck, as well as in peripheral organs. In particular it has been described in the sellar region, external auditory canal, mastoid, tongue, thyroid and thyroglossal duct, parathyroid glands, lung and breast (14,15,16,17). This ectopic tissue may give birth to the same neoplasms which commonly affect salivary glands.
As far as we know, we reported the first case of EMCC arising in Meckel's cave. Meckel's cave is not usually the site of salivary gland tissue, nor heterotopia has been ever described. In the histological slides obtained in the present case, no normal salivary gland tissue was present. Nevertheless, on the basis of the neuroradiological and clinical features, the most plausible hypothesis is that the present EMCC originated from salivary gland heterotopia in Meckel's cave.
Despite its rarity, EMCC should be considered in patients with MRI signs of a base skull mass presenting with neurological symptoms related to progressive cranial nerves involvement. The definitive diagnosis is obviously histological but there are some radiological and clinical signs that can lead to suspect a neurotropic epithelial tumor. In particular, in our case, elements excluding more common inflammatory or lymphoproliferative etiologies were the slow rate of symptoms progression, the normal blood and CSF biochemical profile, concomitantly with the poor response to high dose corticosteroids. The MRI features more consistent with EMC were the T2 slight hyperintense appearance and the diffuse and intense contrast enhancement following the course of the cranial nerves sheets.
Due to its rarity there is no consensus regarding the optimal treatment of EMCC (3). Wide surgical excision with clean margins is recommended if possible. Adjuvant radiotherapy is often required, particularly for neoplasms with a large diameter at risk for local recurrence (3,17,18). In our case, it was not possible to achieve a gross total resection due to the involvement of multiple regions of the skull base, the perineural extension of the tumor and the close contact with the carotid artery, exposing the patient to risks of injuries of the vessel or of permanent CN palsy. Indeed, a biopsy could be performed only after the second MRI that showed extension in the pterygopalatine fossa. However, the post-radiotherapy outcome of the patient was good, confirming the well described radio-sensitivity of this neoplasm. The utility of chemotherapy in treating EMC remains not well established (17, 18).
REFERENCES
Contributed by Matteo Foschi, Giovanni Rizzo, Matteo Zoli, Diego Mazzatenta, Frederica Marliani, Maria Pia Foschini, Patrizia Avoni, Rocco Liguori