An otherwise healthy two-month-old female C57BL/6J mouse presented with a left-sided head tilt. Differential diagnoses included idiopathic necrotizing arteritis, bacterial otitis media/interna (Pasteurella pneumotropica, Pseudomonas aeruginosa, Streptococcus sp., Mycoplasma pulmonis and Burkholderia gladioli), encephalitis, an abscess, neoplasia, a congenital malformation and an accidental or iatrogenic head trauma. Magnetic resonance imaging (MRI) revealed a large space-occupying right olfactory lobe intra-axial lesion with severe secondary left-sided subfalcine herniation. Following imaging, the animal was euthanized due to poor prognosis. Histopathologic examination revealed a unilateral, full-thickness bone defect at the base of the cribriform plate and nasal conchae dysplasia, resulting in the herniation of the olfactory bulb into the nasal cavity. There was also a left midline-shift of the frontal cortex and moderate catarrhal sinusitis in the left mandibular sinus. The MRI and histopathologic changes are consistent with a congenital malformation of the nasal cavity and frontal aspect of the skull known as an ethmoidal meningoencephalocele. Encephaloceles are rare abnormalities caused by herniation of contents of the brain through a defect in the skull which occur due to disruption of the neural tube closure at the level anterior neuropore or secondary to trauma, surgical complications, cleft palate or increased intracranial pressure. The etiology is incompletely understood but hypotheses include genetics, vitamin deficiency, teratogens, infectious agents and environmental factors. Ethmoidal encephaloceles have been reported in multiple species including humans but have not been reported previously in mice. There are multiple models for spontaneous and induced craniofacial malformation in mice, but none described for ethmoidal encephaloceles.

一只健康的两个月大雌性 C57BL/6J 小鼠出现左侧头部倾斜。鉴别诊断包括特发性坏死性动脉炎、细菌性中耳炎/内耳炎（嗜肺巴氏杆菌、铜绿假单胞菌、链球菌、肺支原体和剑兰伯克霍尔德杆菌）、脑炎、脓肿、肿瘤、先天性畸形和意外或医源性头部外伤。磁共振成像（MRI）显示右侧嗅叶轴内有一个大的占位病变，并伴有严重的继发性左侧镰下疝。成像后，由于预后不良，该动物被安乐死。组织病理学检查显示筛板底部存在单侧全层骨缺损和鼻甲发育不良，导致嗅球突出进入鼻腔。额叶皮质向左中线移位，左下颌窦出现中度卡他性鼻窦炎。 MRI 和组织病理学变化与鼻腔和颅骨额部的先天性畸形（称为筛骨脑膜脑膨出）一致。脑膨出是一种罕见的异常现象，是由于前神经孔水平的神经管闭合破坏或继发于创伤、手术并发症、腭裂或颅内压升高而导致的脑内容物通过颅骨缺损突出而引起的。其病因尚不完全清楚，但假设包括遗传、维生素缺乏、致畸、传染源和环境因素。 筛状脑膨出已在包括人类在内的多个物种中报道过，但此前尚未在小鼠中报道过。小鼠自发性和诱发性颅面畸形有多种模型，但没有描述筛骨脑膨出的模型。