The line dividing the anterior and middle skull base can be drawn along the posterior aspect of the lesser sphenoid wing and along the posterior aspect of the planum sphenoidale, which (depending on the source used) typically does not include the anterior clinoid processes ( 6– 9). Posteriorly, the flat surface of the planum sphenoidale separates the sphenoid sinus from the intracranial contents. Laterally, the ASB is composed of the orbital plates of the frontal bones and anteromedially by the cribriform plate, crista galli, and fovea ethmoidalis of the ethmoid bone. The ASB is formed by the ethmoid, frontal, and sphenoid bones. Blue = masticator space, dark yellow = parotid space, fuchsia = parapharyngeal space, green = nasal cavity, light yellow = maxillary sinus, pink = carotid space, purple =perivertebral space, red = spinal canal and spinal cord, teal = nasopharynx. (c) Axial CT image with color-coded overlay shows the extracranial spaces. Blue = temporal bones, fuchsia = nasal bones, green = ethmoid bone, light pink = vomer, purple = occipital bones, teal = sphenoid bone, yellow = zygomatic bones. (b) Axial CT image with color-coded overlay shows the skull base bones. Blue = central skull base (CSB), purple = posterior skull base, teal = anterior skull base (ASB). (a) Axial three-dimensional reconstructed CT image with color-coded overlay shows the skull base sections. The bones and foramina of the skull base can be segmented into three main components: anterior, middle, and posterior ( Figs 2, 3) ( 6– 9).įigure 1a. Arteries, veins, and multiple cranial nerves traverse the skull base through a constellation of canals and foramina. It is formed from portions of the frontal, ethmoid, sphenoid, paired temporal, paired parietal, and occipital bones ( Fig 1). The skull base separates the intracranial and extracranial compartments. At our trauma center, in addition to obtaining CT images with 5-mm section thickness, we routinely obtain 0.625-mm thin-section images by using a bone algorithm with sagittal and coronal reformatted images for all trauma head CT protocols, thereby enhancing the depiction of complex skull base anatomy. In addition to obtaining directly acquired axial images, high-resolution multiplanar reformatted images, including those obtained in the coronal and sagittal planes, may be constructed from the axial dataset to increase sensitivity in the acute setting ( 2, 5). Obtaining thin-section images of 3 mm or less is recommended in the setting of trauma, as use of thick-section images has been found to miss a significant number of linear fractures and skull base lesions, particularly when the images are obtained in the horizontal plane ( 3, 4). Studies have shown the superiority of depicting findings on thinly collimated spiral CT images ( 2). An interpretation checklist to help improve diagnostic accuracy is provided.Īccording to the practice parameter for the performance of head CT developed by the American College of Radiology, the American Society of Neuroradiology, and the Society for Pediatric Radiology ( 1), contiguous or overlapping axial images should be acquired with a section thickness of no greater than 5 mm. We review the imaging characteristics of important “do not miss” lesions at the skull base on the basis of their anatomic location and manifestations. In this article, we review and illustrate the essential skull base anatomy and the common blind spots important to radiologists interpreting a nonenhanced head CT study in the acute setting. Delayed diagnosis, misdiagnosis, or lack of recognition of skull base conditions can negatively impact patient care, highlighting the importance of using a mental checklist when interpreting studies of the skull base, especially the first few images of the study. These neurologic manifestations are often referred to as red flags and include cranial nerve deficits, strokelike symptoms that are atypical for a specific vascular territory, and progressive and/or recurrent onset of symptoms. In addition, using a systematic search pattern and having an overall awareness of the neurologic manifestations of a skull base lesion can aid in increasing the diagnostic yield for the interpreting radiologist. Therefore, all radiologists working in the acute care setting must have a thorough knowledge of normal skull base anatomy at CT and the wide spectrum of disease that may manifest in this area. Skull base anatomy is complex, and pathologic conditions in this region can be subtle and easily overlooked. Routine head CT often includes images of portions of the skull base, extracranial spaces, and upper cervical spine. Non–contrast material–enhanced CT of the head is the primary imaging modality used to evaluate patients with neurologic deficits who present to the emergency department.

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