Petrous Apex Lesions
Endoscopic SkullBase Surgery
Petrous Apex Lesions
Petrous bone is part of the temporal bone. It is pyramidal in shape and is wedged between the greater wing of sphenoid and basiocciput (Fig.1). The inner ear (cochlea & labyrinth) is within the petrous bone. The tip of the pyramidal bone (medial to cochlea and internal auditory canal) is filled with marrow and is pneumatized in 33%. Pneumatization (presence of air spaces within the bone) of the petrous apex results from extension of air cells from mastoid around the labyrinth to the petrous apex. This provides direct pathways for disease to spread from the mastoid bone or middle ear to the petrous apex. Pneumatization is asymmetric in 5%–10% of individuals.
Fig.1. : Picture of skull base. Petrous bone is coloured green. IAM – internal auditory meatus. JF – jugular fossa. Triangular area marked is the petrous apex.
The apex of the petrous bone lies in a complex anatomic region that contains a number of critical neural and vascular structures. Therefore, lesions arising in or spreading to the petrous apex cause varied and occasionally severe clinical sequelae, which typically are the result of mass effect or direct invasion of the cranial nerves, brainstem, or internal carotid artery (ICA).
A variety of pathology occurs at petrous apex. Before the advent of antibiotics, infections of the petrous apex was common and progressed to meningitis, brain abscess and death. Since the introduction of antibiotics, the prevalence of such serious complications has been drastically reduced. Eventhough rare, the most common pathology encountered at present is cholesterol granuloma and it forms 60% of all lesions in this area. Other lesions seen in this area are congenital cholesteatoma, mucocoele, encephalocoele and tumours like meningioma, schwannoma. Chondrosarcoma and chordoma.
The diagnosis usually isn’t based on a biopsy, because it’s so hard to get to. It’s in the middle of the head. So we do rely a lot on imaging.
Management of petrous apex pathology poses a unique challenge even to the most experienced skull base surgeons. The central location in the skull base with adjacent critical neurovascular structures makes access to this region more than a trivial matter.
The introduction of modern skull base surgery techniques also has provided skull base surgeons with numerous avenues to the petrous apex while significantly decreasing morbidity.
Solid tumors/cholesteatoma removed when first identified, rather than after symptoms develop. Establish outflow drainiage pathway that is maintained so that cholesterol granuloma expansion does not result in recurrence of
patient’s symptoms. Small cystic lesions can be observed with periodic MRI to assess the growth. Delaying surgery in presence of symptoms offers no real advantage
- We need to consider the following before choosing the surgical approach.
- Patient’s hearing level
- Drainage of a cyst or excision of a tumour
- Pneumatization of the temporal bone and sphenoid
If the petrous apex lesion is lateral to the paraclival carotid artery (Fig.2), it can’t be accessed endoscopically through the nose. If the sphenoid sinus is well pneumatized and is abutting the petrous apex, and the lesion extends medial to the paraclival carotid artery (Fig.3) it can be approached through the nose using endoscope. It gives wide drainage pathway and is done without retracting the brain. This is the treatment of choice. Further access laterally along and parallel to horizontal petrous carotid can be obtained by going through the contralateral maxillary antrum (Fig.4).
Fig.2. : Lesion lateral to paraclival carotid artery
Fig.3. : Lesion extending medial to paraclival carotid artery
Fig.4. : Extended contralateral transmaxillary corridor to petrous apex
If it is extension of infection from mastoid, petrous apex can be drained through the air cell tract underneath or infront of cochlea.
If the petrous apex lesion is not projecting into the sphenoid sinus, the middle cranial fossa approach / infratemporal approach / transcochlear approach may be used in resecting tumours or tumour-like conditions.
The Heart Of Clinic
Dr. C. Rayappa MBBS, DLO, FRCS(Edin)
SENIOR CONSULTANT
+91 44 3315 1105
Dr. C. Rayappa graduated from Madras Medical College, Chennai, India in 1982. He completed his post graduation in Otolaryngology (ENT)
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The Heart Of Clinic
Dr. C. Rayappa MBBS, DLO, FRCS(Edin)
SENIOR CONSULTANT
+91 44 3315 1105
Dr. C. Rayappa graduated from Madras Medical College, Chennai, India in 1982. He completed his post graduation in Otolaryngology (ENT)