Oral squamous cell carcinoma (OSCC) is one of the leading presentations of head and neck cancer (HNC). The first part of this review will describe the highlights of the oral microbiome in health and normal development while demonstrating how both the oral and gut microbiome can map OSCC development, progression, treatment and the potential side effects associated with its management. We then scope the dynamics of the various microorganisms of the oral cavity, including bacteria, mycoplasma, fungi, archaea and viruses, and describe the characteristic roles they may play in OSCC development. We also highlight how the human immunodeficiency viruses (HIV) may impinge on the host microbiome and increase the burden of oral premalignant lesions and OSCC in patients with HIV. Finally, we summarise current insights into the microbiome–treatment axis pertaining to OSCC, and show how the microbiome is affected by radiotherapy, chemotherapy, immunotherapy and also how these therapies are affected by the state of the microbiome, potentially determining the success or failure of some of these treatments.

Eagle's Syndrome (ES) refers to a symptomatic anomaly due to elongation of the styloid process or mineralization of the styloid complex. If not diagnosed timely and treated properly, elongation of the styloid process or the hyper-mineralization of the stylohyoid ligament may eventually lead to complete ossification of the stylohyoid complex. Non-specific head and neck symptoms of the ES may pose diagnostic challenges to the clinician. Therefore it is crucial to include ES among differential diagnosis when evaluating patients with similar head and neck symptoms. Once the diagnosis is confirmed, treatment plan should be tailored in accordance with the individual requirements of the case and performed without delay. Both pharmacological and surgical methods have been described for the treatment of the patients with ES. However for those who suffer from persistent symptoms, surgical removal of the elongated styloid process is the treatment of choice and can be done with an intraoral or an extraoral approach. The aim of this work is to present unusual clinical symptoms and radiologic findings of ES due to complete ossification of the stylohyoid complex. The importance of a correct diagnosis and appropriate treatment are highlighted.Keywords Eagle's Syndrome Á Ossification Á Stylohyoid Á Hypoglossal nerve palsy HistoryA 48-year-old female patient with non-significant past medical history was referred for evaluation and management of unilateral weakness of her tongue. Among her initial complaints were sharp lancinating pain on swallowing, altered speech, dry mouth, left neck swelling, and intermittent loss of taste. Radiographic FeaturesInitial radiographic examination was carried out with a panoramic radiograph, which revealed a voluminous ossified stylohyoid complex on the patient's left side (Fig. 1). Computerized tomography (CT) imaging was obtained to further evaluate the true dimension and angulation of the calcified tissue. Sagittal view (Fig. 2) and the threedimensional CT reconstruction (Fig. 3) demonstrated complete ossification of the stylohyoid complex. DiagnosisClinical examination of the patient revealed a fixated mass, which was firm on palpation in the left submandibular

Lugol's iodine staining can effectively be used in detection of the dysplastic and malignant superficial lesions of the oral epithelium.

Graphical abstract

There are an estimated 6–10 million smokeless tobacco (Toombak) users in Sudan, the majority being males. Toombak is known to be a carcinogenic product that is likely to modify the oral microbiome spatiality into a high-risk potential for the development and progression of oral cancer, but previous studies are lacking in this field. Here, we endeavour for the first time the exploration of the oral microbiome in key mucosal areas of the oral cavity and assess the microbiome variations in premalignant and oral squamous cell carcinoma (OSCC) samples from both users and non-users of Toombak. 16S rRNA sequencing was performed on DNA obtained from pooled saliva, oral mucosa and supragingival plaque from 78 Sudanese users and non-users of Toombak, aged between 20 and 70 years. In 32 of the pooled saliva samples, the mycobiome (fungal) environment was analysed through ITS sequencing. Then, 46 formalin-fixed paraffin-embedded samples of premalignant and OSCC samples were collected, and their associated microbiomes sequenced. The oral Sudanese microbiome was found to be enriched in Streptococcaceae, but Staphylococcaceae were significantly more abundant amongst Toombak users. Genera enriched in the oral cavity of Toombak users included Corynebacterium_1 and Cardiobacterium while in non-users, Prevotella, Lactobacillus and Bifidobacterium were prominent. Aspergillus was the most abundant fungus in the mouths of Toombak users with a marked loss of Candida. The genus Corynebacterium_1 was abundant in the buccal, floor of the mouth and saliva microbiomes as well as in oral cancer samples from Toombak users indicating a possible role for this genus in the early stages of oral cancer development. An oral cancer microbiome that favours poor survival and metastasis in those who use Toombak also emerged that includes the genera Stenotrophomonas and Schlegelella. Those utilising Toombak carry an altered oral microbiome that may be an additional risk factor for this products carcinogenicity to the oral structures. These significant microbiome modulations are a newly emerging key driving factor in oral cancer development and progression in Toombak users while it is also shown that Toombak users carry an oral cancer microbiome that may increase the potential for a poorer prognosis.