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Thread: Picture of Surgical Approaches to the Petrous Apex pictures - Ear Atlas

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    Default Picture of Surgical Approaches to the Petrous Apex pictures - Ear Atlas

    The three cranial fossae of the skull base are situated at different levels: the anterior fossa is at a higher level than the posterior fossae. The petrous portion of the temporal bone separates the middle fossa from the posterior fossa, and its apex is located deep and is related to important neurovascular structures.

    The petrous apex is a pyramid-shaped bone with three surfaces: anterior, posterior, and inferior. The anterior surface is limited by the foramen lacerum, sphenopetrous fissure, facial nerve hiatus, and arcuate eminence. The posterior surface is limited by the petro-occipitalis fissure (inferior petrosal sinus sulcus), the superior lip of the jugular foramen, and the posterior border of the internal auditory canal. The inferior surface of the petrous apex is limited by the foramen lacerum, petro-occipitalis fissure, medial lip of the carotid canal, and sphenopetrous fissure. These three surfaces point to the clivus region posteroanteriorly.2 Gianoli and Amedee (1994)3 also described the petrous apex as a pyramidal segment and divided this structure in two parts through the internal auditory canal. The anterior portion is related to the auditory tuba, the major superficial petrous nerve, the trigeminal nerve, the cavernous sinus, and the internal carotid artery. The posterior portion, formed by dense bone, is located between the internal auditory canal and semicircular canals.

    Most of the multidisciplinary approaches to the skull base were developed in the 1980s. These combined strategies improve the results of the surgical removal of petrous bone and petrous apex lesions.

    Petrous apex lesions may be approached surgically in different ways. The choice of approach is determined by the extent and nature of the pathology, by the patient's preoperative clinical condition, and by the surgeon's experience. The distance between the craniotomy and petrous apex also may be an important factor in choice of surgical access.

    Skull morphology varies among individuals. Although the topic has been discussed at skull base surgery congresses, the influence of skull morphology on the choice of the surgical approaches has not been reported. This was the objective of the present study.

    Eighty-four dry human skulls and 1503 computed tomographic (CT) films were analyzed. Sixty-five dry human skulls were measured at the Departments of Anatomy of the Universidade Federal do Paraná, Pontifícia Universidade Católica do Paraná, and Universidade Tuiuti do Paraná with the written permission of each department's chairperson. A pachymeter and a millimetrically graduated ruler were used for measurements (Fig. 1). Nineteen dry skulls were excluded for not fulfilling the measurement criteria: integrity of the cranial bone, bilateral symmetry of cranial structures, and presence of reference structures (i.e., posterior clinoid process, petrous pyramid).
    Picture Surgical Approaches Petrous Apex attachment.php?s=73d055ef6b9d2c8c259be5a5663776b5&attachmentid=1859&d=1441390122

    The CT scans were analyzed and measured at Centro de Diagnóstico por Imagem do Paraná (CEDIP), authorized by the directors of the center under discretion policy. CT scans were obtained with a General Electric (USA) Sytec 3000 scanner with transverse cuts parallel to the orbit meatal plane. Three hundred and one images were measured, and 1203 examinations were excluded for not fulfilling the following criteria: patient's age (18 and older), integrity of the cranial bone, orbitomeatal plane of the image (examinations not parallel to the orbitomeatal plane were excluded), or bilateral symmetry of the cranial reference structures (posterior clinoid process and petrous pyramid).

    The parameters measured were maximal length and width of the skulls and the distances from the entry point of the different surgical approaches (i.e., pterional, subtemporal, presigmoid, and retrosigmoid) to the petrous apex (see Fig. ​Fig.2).2). The left side of the brain was measured in all images and skulls, and this was an aleatory choice. All measurements were performed from the external cortical table of the skull. The reference point for the location of the petrous apex was the posterior clinoid process, which delimits the sella turcica posteriorly due to its easy visualization on the CT scans.

    Medical Therapy
    Petrous apicitis (as seen in the CT scan images below) is an inflammatory process often secondary to suppurative otitis media. Medical therapy is aimed at eliminating bacterial infection and promoting drainage with aggressive antibiotic therapy. Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus are the primary pathogens responsible for petrositis. Steroids may help decrease inflammation, pain, and swelling. Early surgical intervention is critical because of the severe complications secondary to chronic otitis media and petrous apicitis
    Petrous apicitis. An axial CT scan of the temporal bone shows an air-fluid level within the right petrous apex and fluid within the middle ear space and mastoid.
    Skull base osteomyelitis is primarily a medical disease requiring long-term antimicrobial therapy directed against Pseudomonas aeruginosa. Severe otitis externa with granulation tissue in an immunosuppressed patient is the most common clinical setting. Often, the pain is described as deep and boring, with this symptom seeming out of proportion to physical findings. Aminoglycosides, coupled with an antipseudomonal penicillin derivative, are the antibiotics of choice. Quinolone antibiotics offer enteral therapy with encouraging results. Gallium-67 scanning is used to monitor the course of the disease. Technitium-99 scanning is more specific in the diagnosis, but findings remain positive after the course of the disease so they cannot be used to monitor therapy.

    Surgical Therapy
    With the exception of petrous apicitis and skull base osteomyelitis, all lesions of the petrous apex are best treated surgically. Preoperative histologic diagnosis or strong clinical suspicion is critical to making the proper surgical plan. The availability of an experienced and skilled neuroradiologist is critical in making a confident and accurate preoperative assessment. Ask to have the films read elsewhere if the preoperative imaging studies are inconclusive or vague. The diversity of apex lesions does not permit characterization of the surgical approach. The specific surgical techniques are discussed in Intraoperative details.

    Preoperative Details
    Careful preoperative evaluation is critical in minimizing intraoperative and postoperative complications. Neurologic examination allows a thorough understanding of preoperative deficits. Preoperative imaging studies define the exact size and location of the lesion. Angiography determines the vascular supply of the particular lesion and helps to narrow the differential diagnosis to assist in choosing the best treatment approach while avoiding complications. Autologous blood or donor-directed blood availability is addressed preoperatively. Often, central venous monitoring and arterial monitoring are helpful in the intraoperative and postoperative period.
    Picture Surgical Approaches Petrous Apex attachment.php?s=73d055ef6b9d2c8c259be5a5663776b5&attachmentid=1860&d=1441390135

    Middle fossa
    William House popularized the middle fossa approach as a method of excising acoustic neuromas while preserving hearing. Others described this approach to access the petrous apex. Intracanalicular tumors smaller than 1.5 cm and serviceable hearing are approached through the middle fossa in some centers. The criterion for middle fossa approach in acoustic surgery has expanded to include larger tumors with some extension into the cerebellopontine angle. Facial neuromas, facial hemangiomas, trigeminal neuromas, cholesterol granulomas, congenital and acquired cholesteatomas, and some petroclival meningiomas can also be approached through the middle fossa subtemporal craniotomy.

    The transcochlear approach described by House is essentially an anterior extension of the translabyrinthine approach. After a translabyrinthine approach is performed, the greater superficial petrosal nerve is cut anteriorly to the geniculate ganglion, and the nerve is taken out of its bony canal from the proximal internal auditory canal to the stylomastoid foramen. The facial nerve is reflected posteriorly, and the bony cochlea is removed with a drill. The anterior extent of the bony dissection is the petrous portion of the carotid artery. The procedure provides excellent exposure but leaves the patient with anacusis in the operated ear. Often, return of facial function is incomplete because of the extensive nerve manipulation. Meningiomas and cholesteatomas, especially when the hearing is already compromised, are often resected by this approach.

    Surgical Approaches to the Petrous Apex: Distances and Relations with Cranial Morphology

    Last edited by Medical Photos; 09-04-2015 at 06:08 PM.

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