Petrous apicitis

Clinical History

A 3-year-old boy was admitted to the emergency department with strabismus. Physical examination disclosed left abducens nerve palsy. The patient had experienced a viral gastrointestinal infection two weeks before admittance. An emergency MR imaging study was performed, followed by a temporal bone high resolution CT.

Imaging Findings

Axial T1- and T2-weighted images show an abnormal left petrous apex, with partial diffusion restriction on DI and ADC mapping. Contrast-enhanced axial and coronal T1 images demonstrate an enhancing soft tissue within the lesion. There is no large soft tissue lesion suggestive of malignant disease.
Axial high-resolution CT of the temporal bone obtained with bone algorithm demonstrates the osteolytic lesion involving the left petrous apex. Extension of the lesion into the adjacent sphenoidal clivus is more notable than on the previous MR imaging procedure. Scintigraphy was also performed to rule out other bony lesions. FDG-PET/CT only showed increased FDG uptake in the left petrous apex.

Discussion

Background
In 1904 Guiseppe Gradenigo described an infection of the apex of the petrous part of the temporal bone from acute otitis media with the clinical symptoms of unilateral pain around the eye, diplopia due to sixth nerve paralysis and persistent otorrhoea. The facial pain is due to focal meningitis over the petrous apex with irritation of the gasserian ganglion in the Meckel cavity. Abducens nerve involvement occurs at its course through the Dorello canal [2, 3].
Clinical Perspective
Today, because of the intense antibiotic treatment used in acute otitis media, the clinical signs of petrositis may be less typical compared to former times. Although sixth nerve palsy is considered the least reliable sign, a case was reported similar to ours, in which it was the sole presenting symptom.
Imaging Perspective
CT usually demonstrates opacification of the petrous apex, with destruction of septae and overlying cortex. There is also pathological enhancement extending to the meninges and Meckel's cave. MR imaging better demonstrates such enhancement and it is essential for investigating intracranial complications, including venous thrombosis.
The main differential diagnosis for this case include Langerhans’ cell histiocytosis, in which involvement of the temporal bone has been described in 15% to 61% of all cases, most commonly occurring during the course of multisystemic disease. CT often shows extensive destruction, with indistinct margins and an associated enhancing soft-tissue mass. Disease limited to the apex of the petrous bone is very rare although a few cases have been reported. Malignant lesions, mainly rhabdomyosarcoma, manifest as aggressive lesions of the petrous apex with a lytic or permeative destruction on CT. MRI findings are frequently nonspecific. Cholesterol granuloma is the most frequent surgical lesion in the petrous apex, with a characteristic increased signal on T1- and T2- weighted images. Diffusion-weighted imaging is very useful for differentiating other cystic lesions from cholesteatoma, owing to restricted diffusion of the latter.
Outcome
Treatment usually consists of mastoidectomy and antibiotics, but children are often managed with medication and have a positive outcome.
In our particular patient, based on demonstration that the petrous abnormality was a single lesion and the blood sample normal, the child received intravenous antibiotic therapy. The left abducens nerve palsy quickly improved and completely disappeared within two weeks.
Take Home Message
Be aware of acute strabismus and abducens nerve palsy in a child. Carefully look for a lesion involving petrous apex, either on CT (better with high resolution and bone windowing) or preferentially on MR imaging.

Differential Diagnosis List

Final Diagnosis

Petrous apicitis

URL:	https://www.eurorad.org/case/9004
DOI:	10.1594/EURORAD/CASE.9004
ISSN:	1563-4086