Background This study aimed to analyze whether immunohistochemistry (IHC) is more sensitive than hematoxylin-eosin (H&E) staining for identifying perineural invasion (PNI) or lymphovascular invasion (LVI) in oral squamous cell carcinoma (OSCC). Material and Methods In this systematic review and meta-analysis (Prospective Register of Systematic Reviews – CRD 42021256515), data were obtained from six databases (PubMed, Scopus, LILACS, Web of Science, EBSCO, LIVIVO, Embase) and the grey literature. Cross-sectional observational studies of the diagnostic sensitivity of IHC for PNI and LVI were included. Studies were selected in two phases: first collection and reference retrieval. The Quality Assessment of Diagnostic Accuracy Studies-2 tool assessed study quality, while the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach assessed evidence quality. The meta-analysis (random effects model) was performed using MedCalc 18.2.1 software (MedCalc®) ( p <0.05). Results Four studies (560 patients with 295 biopsies) were analyzed. The combined sensitivity was 76% (95% confidence interval [CI], 44.30–97.19%) and specificity was 42% (95% CI, 23.40–62.02%). The positive predictive value (PPV) and negative predictive value (NPV) were 61% (95% CI, 49.78–71.53%) and 70% (95% CI, 37.63–94.43%). The overall accuracy was 58% (95% CI, 45.17–70.65%). The risk of bias was low, and GRADE analysis showed a very low certainty of evidence. Conclusions Our data suggest that IHC staining to highlight PNI/LVI may be useful in cases in which H&E analysis results in a negative decrease in the prevalence of false-negative cases and underestimated treatment. Key words: Mouth neoplasms, neoplasm invasiveness, blood vessels, peripheral nerves.

Langerhans' cell histiocytosis (LCH) comprises a rare group of reticuloendothelial system disorders that can produce focal or systemic manifestations. Diabetes insipidus is considered to be an important indicator of serious underlying diseases in children, including LCH. We report the case of a young patient with monostotic LCH confined to the mandibular ramus, who was diagnosed with the disease after presenting symptoms of central diabetes insipidus and was satisfactorily treated with multi-agent chemotherapy. Additionally, we discuss the clinical, radiographic, histological and immunohistochemical findings, as well as the multidisciplinary approach of this important disease, which should receive attention by dental practitioners, especially when it occurs in children.