The petrous apex represents the pyramidal shaped medial portion of the temporal bone located between the inner ear structures laterally, petrosphenoidal fissure and internal carotid artery (ICA) anteriorly, petro-occipital fissure medially and the posterior cranial fossa behind. The superior surface is formed by the middle cranial fossa, Meckel cave, and ICA. Along the inferior surface are the jugular bulb and inferior petrosal sinus.

The petrous apex is subdivided by the internal auditory canal (IAC) into an anterior (larger, typically contains bone marrow) and a posterior portion (smaller and denser in appearance).

The petrous apex houses important vascular and neuronal channels: ICA, IAC, Dorello’s, singular, and arcuate canals [1]. (Figures 1-3).

PAL may cause severe clinical sequelae, which typically result from mass effect or direct invasion of the cranial nerves, brainstem, or internal carotid artery. 

Differential diagnosis of PAL includes a wide spectrum of disorders with variable prognosis and outcomes. Among them there are surgical and medical causes that require an early diagnosis and treatment. However, there are normal variants that should not be mistaken with these lesions. 

We classify them on the basis of their origin into developmental (cholesterol granuloma, cholesteatoma...), inflammatory/infectious (apicitis, osteomyelitis), neoplastic (benign or malignant) and vascular lesions.

MR imaging is the first-line study for evaluation of PAL since it provides excellent delineation of the soft tissue extent of lesions and relationship to nearby structures. CT allowes characterization of petrous apex pneumatization, mineralization and osseous involvement [2,3].