The Petrous Apex

Petrous apex pneumatisation in children: a radiological study

OBJECTIVE

This study aimed to investigate petrous apex pneumatisation in children, as an understanding of petrous apex pneumatisation is useful in the diagnosis and surgical management of middle-ear disease.

METHODS

Computed tomography head scans from 1700 patients aged 0-16 years were assessed. Petrous apex bone and air cell volumes were calculated to determine the degree of petrous apex pneumatisation. Scans were analysed for communicating tracts between the middle ear and petrous apex.

RESULTS

Petrous apex pneumatisation was found in 21.0 per cent of patients. Positive relationships were found between age and petrous apex pneumatisation prevalence (rs = 0.990, p < 0.001), and between age and degree of petrous apex pneumatisation (rs = 0.319, p < 0.001). Petrous apex pneumatisation prevalence did not significantly differ by sex or ethnicity. Communicating tracts were identified in 84.3 per cent of patients with petrous apex pneumatisation, most commonly anterior to the otic capsule.

CONCLUSION

In children, the prevalence and degree of petrous apex pneumatisation increases with age, but prevalence is not affected by sex or ethnicity.

Analysis of various tracts of mastoid air cells related to CSF leak after the anterior transpetrosal approach

OBJECTIVE

The anterior transpetrosal approach (ATPA) was established in 1984 and has been particularly effective for petroclival tumors. Although some complications associated with this approach, such as venous hemorrhage in the temporal lobe and nervous disturbances, have been resolved over the years, the incidence rate of CSF leaks has not greatly improved. In this study, some varieties of air cell tracts that are strongly related to CSF leaks are demonstrated. In addition, other pre- and postoperative risk factors for CSF leakage after ATPA are discussed.

METHODS

Preoperative and postoperative target imaging of the temporal bone was performed in a total of 117 patients who underwent ATPA, and various surgery-related parameters were analyzed.

RESULTS

The existence of air cells at the petrous apex, as well as fluid collection in the mastoid antrum detected by a postoperative CT scan, were possible risk factors for CSF leakage. Tracts that directly connected to the antrum from the squamous part of the temporal bone and petrous apex, rather than through numerous air cells, were significantly related to CSF leak and were defined as “direct tract.” All patients with a refractory CSF leak possessed “unusual tracts” that connected to the attic, tympanic cavity, or eustachian tube, rather than through the mastoid antrum.

CONCLUSIONS

Preoperative assessment of petrous pneumatization types is necessary to prevent CSF leaks. Direct and unusual tracts are particularly strong risk factors for CSF leaks.

Petrous apex lesions in the pediatric population

A variety of abnormal imaging findings of the petrous apex are encountered in children. Many petrous apex lesions are identified incidentally while images of the brain or head and neck are being obtained for indications unrelated to the temporal bone. Differential considerations of petrous apex lesions in children include "leave me alone" lesions, infectious or inflammatory lesions, fibro-osseous lesions, neoplasms and neoplasm-like lesions, as well as a few rare miscellaneous conditions. Some lesions are similar to those encountered in adults, and some are unique to children. Langerhans cell histiocytosis (LCH) and primary and metastatic pediatric malignancies such as neuroblastoma, rhabomyosarcoma and Ewing sarcoma are more likely to be encountered in children. Lesions such as petrous apex cholesterol granuloma, cholesteatoma and chondrosarcoma are more common in adults and are rarely a diagnostic consideration in children. We present a comprehensive pictorial review of CT and MRI appearances of pediatric petrous apex lesions.

[Radiological diagnostic of the non-pathological conditions of the petrous apex]

Many patients with otological symptoms are remitted to the otolaryngology outpatient clinics every day. These patients commonly undergo imaging studies, generally magnetic resonance imaging (MRI). In some cases, a positive unilateral result is found in the form of a potentially pathological signal that can be observed in the petrous apex region. We present the cases of 6 patients (aged between 26 and 62 years) with asymmetric bone marrow distribution or trapped mucous fluid secretions in the petrous apex, collected over a 6-year period. Diagnosis was made with the use of CT scans and MRI. All of the patients were referred for skull base surgery. In all cases a non-pathologic asymmetry was diagnosed in the petrous apex. Certain non-pathologic conditions of the petrous apex must be treated expectantly without any surgery.

CT versus MR: still a tough decision

CT and MRI are the two most widely used imaging modalities for evaluating head and neck pathology. There is continued controversy in the literature about which modality is superior for imaging different areas of the head and neck. This article summarizes the literature supporting the use of CT, MRI, or both for specific clinical scenarios in otolaryngology. Familiarity with the benefits and potential pitfalls of each modality allows referring physicians and radiologists to tailor imaging regimens to the needs of individual patients.

Endonasal endoscopic approach to the petrous apex: an image-guided quantitative anatomical study

BACKGROUND

The petrous apex is a relatively inaccessible region, deeply situated within the skull base. Removal of lesions from this area, traditionally accomplished via lateral approaches, can cause significant morbidity. We undertook an anatomical study to investigate the surgical anatomy of the petrous apex through an endonasal endoscopic approach, which has been sporadically described in the literature, to investigate its feasibility and to characterise clear and consistent surgical landmarks for access.

METHODS

Cadaveric dissections were performed on five heads. Pre-dissection computed tomography scans were used, with the BrainLab navigation system, to verify entry into the petrous apex. Surgical landmarks were characterised in relation to fixed sphenoid sinus structures, and surgical access before and after drilling the sphenoid sinus rostrum was quantitatively compared.

RESULTS

The landmark for entry into the petrous apex was the intersection of a vertical line halfway between the medial surface of the internal carotid artery and the midline, with a horizontal line one-third of the way up from the postero-inferior floor of the sphenoid sinus. The dimensions of the postero-superior sphenoid sinus were characterised by the inter-carotid distance, pituitary-to-sphenoid-floor distance and the width of the sphenoid sinus floor, which were 15 +/- 3 mm, 16 +/- 3 mm and 26 +/- 1.6 mm respectively. The surface area of surgical access was 193 +/- 28 mm(2), increasing to 316 +/- 39 mm(2) after drilling of the sphenoid rostrum (P < 0.001; paired t-test).

CONCLUSIONS

Endoscopic approach to the petrous apex is anatomically feasible, and, aided by image navigation, could extend the scope of endonasal surgery to access highly-selected lesions in the middle cranial fossa.

Petrous Apex Effusion: A Clinical Disorder

INTRODUCTION

Petrous apex fluid accumulations without evidence of acute infection are routinely managed as "leave alone lesions" without potential morbidity. Are petrous apex fluid accumulations (effusions) in the absence of acute infection always asymptomatic without the need for treatment? If petrous apex effusions can produce symptoms separate from acute infections, what are the clinical outcomes in these patients?

STUDY DESIGN

Retrospective clinical review.

METHODS

A retrospective record review of 31 patients presenting with petrous apex effusions was performed with recording of clinical characteristics, interventions, and outcomes.

RESULTS

Eighteen of the 31 patients had clinical symptoms referable to the petrous apex effusion with the following characteristics: indolent and previous infections (4), hearing loss (3), headache and pressure alone (8), facial spasms (1), and positional vertigo (2). Overall, 5 of 18 symptomatic patients resolved with antibiotics, steroids, or positioning maneuvers. Three of five infracochlear drainages produced symptom resolution. Three of four patients undergoing retrolabyrinthine drainage had symptom resolution, and four of seven middle fossa drainages yielded symptom resolution. In contrast, infratemporal fossa drainage procedures did not resolve the patients' symptoms.

CONCLUSIONS

Isolated petrous apex effusions are rare, but they can cause symptoms. If medical management fails, surgical drainage based on the location is appropriate. The surgical drainage approach selected (infracochlear, infralabyrinthine, middle fossa, and endoscopic transnasal) should be based on an anatomic consideration of the involved petrous apex air cells (superior vs. inferior) and the relative position of the carotid artery and jugular bulb.

Segmental anatomy of the temporal bone

More of us suffer from hearing loss than from visual impairment, coronary artery disease, and cancer combined. Auditory dysfunction is detected in less than one third of newborns afflicted and is underdiagnosed in the elderly. Despite biomedical and technological advances, our understanding of vestibular dysfunction has grown little. Forming part of the lateral and inferior surfaces of the skull, the temporal bone contains the organs of hearing and balance. Diagnosis of diseases in these important regions requires adequate clinical information and a thorough knowledge of normal temporal bone anatomy to recognize abnormal findings when present. This article dissects the temporal bone into segments, describes the relevant radiologic anatomy of each, and discusses the imaging appropriate to specific concerns.

Incidental Petrous Apex Findings on Magnetic Resonance Imaging

We performed a retrospective chart review to categorize a group of petrous apex findings that were noted incidentally on magnetic resonance imaging (MRI) in 88 patients. These patients were among those who had been seen at a tertiary care center between July 1988 and July 1998. These incidental findings, which were unrelated to the presenting clinical manifestations, included asymmetric fatty bone marrow (n = 41), inflammation (19), cholesterol granulomas (14), cholesteatomas (9), and neoplasms (5). Followup imaging and clinical surveillance of these patients has not demonstrated any significant change in the incidentally detected lesions. In all cases, the incidental MRI findings represented benign pathology.

Imaging destructive lesions of the petrous apex

Cholesterol granuloma and cholesteatoma are the two most common destructive lesions of the petrous apex. Arachnoid cyst is less common. These three expansile lesions are often indistinguishable on clinical grounds. Cholesterol granulomas can be treated effectively through internal drainage into the mastoid cavity or middle ear. Cholesteatomas, however, are managed by more aggressive and complicated removal, which often mandates the sacrifice of hearing. Symptomatic arachnoid cysts are amenable to simple surgical drainage. Therefore, accurate preoperative recognition on computed tomography (CT) and magnetic resonance imaging (MRI) is important in planning proper treatment. Thirteen cases of destructive lesions of the petrous apex are analyzed. The authors' experience illustrates that the "typical" CT and MRI radiographic features are diagnostic in some cases, but not in all. In this study the pathologic findings have been correlated with the radiologic features on both MRI and CT.