Kadish C/Hyams II Esthesioneuroblastoma With Atypical Immunophenotype Mimicking NK/T-Cell Lymphoma: Endoscope-Assisted Transcranial Resection and Adjuvant Intensity-Modulated Radiotherapy

We present a case of an esthesioneuroblastoma (ENB; olfactory neuroblastoma) with an atypical immunophenotype managed by a combined transcranial, endoscope-assisted resection, illustrating diagnostic challenges and surgical decision-making when the anterior skull base and orbit are involved. A 66-year-old woman had recurrent left epistaxis, progressive unilateral nasal obstruction, periorbital pain radiating to the auricle, and ipsilateral visual decline. Examination showed swelling and tenderness over the left nasal region with no lymphadenopathy. Computed tomography (CT) and magnetic resonance imaging (MRI) demonstrated a left sinonasal mass extending to the medial orbit, with erosion of the lamina papyracea and cribriform plate, abutment of the anterior skull base, and molding of the medial rectus without definite intraconal invasion. The initial biopsy suggested natural killer/T-cell (NK/T-cell) lymphoma. Targeted immunohistochemistry (IHC) showed CD56 positivity with a sustentacular S100 pattern, a Ki-67 index of 30%-40%, and negativity for CD3, CD20, granzyme B, T-cell intracellular antigen-1 (TIA-1), chromogranin, and synaptophysin, confirming Kadish C/Hyams II ENB. A bifrontal, endoscope-assisted craniectomy achieved gross total resection and multilayer reconstruction (onlay dural collagen matrix; titanium mesh and polymethylmethacrylate (PMMA) for the anterior skull base; titanium mesh for the orbital roof). Postoperative CT showed no gross residual mass, decompression of the medial rectus, and minimal expected pneumocephalus. Adjuvant intensity-modulated radiotherapy (IMRT) to the surgical bed/anterior skull base was delivered (60 Gy in 30 fractions); elective neck irradiation was individualized. The patient remains stable under multidisciplinary surveillance. Key lessons include broadening the IHC panel to avoid misclassification as NK/T-cell lymphoma when classic neuroendocrine markers are negative, considering a transcranial, endoscope-assisted approach to obtain margins and a stable reconstruction when the anterior skull base/orbit are involved, and obtaining early postoperative imaging as a baseline for surveillance.