Radiological Classification and Management Algorithm of Petrous Apex Cholesterol Granuloma

Abstract

Background: Petrous apex cholesterol granulomas (PACGs) are benign inflammatory cystic lesions of the temporal bone. Usually, asymptomatic patients may develop symptoms as the lesions expand. The diagnosis is based on both CT and MRI scans and the management relies on "wait and scan" or surgery. This paper aims at evaluating surgical outcomes and proposing a CT-based classification and a management algorithm. Methods: Patients with PACGs who were surgically treated between 2014 and 2024 were included. Symptoms, imaging, approach type and complications were considered. CT scans were classified as Type A (preserved apex cellularity), Type B (erosion of the apex cellularity), and Type C (involvement of the noble structures bone boundaries). The possible connection of the lesion with the infracochlear, perilabyrinthine and sphenoidal cellularity was assessed. Results: Nineteen patients with symptoms like diplopia, headache and sensorineural hearing loss were included. According to our classification, 1/19 patients was Type A, 4/19 were Type B and 14/19 were Type C. Five patients underwent a total resection, seven a subtotal and seven a surgical drainage. Only two complications were recorded, and 17/19 patients showed symptom regression and stability during follow-up. Conclusions: While the management of PACGs is still controversial, according to our classification and surgical outcomes, Type A, being mostly asymptomatic, should be managed with "wait and scan", Type B should undergo surgery when symptoms are present, while Type C should always undergo surgery because of their invasiveness and potential complications. When possible, a drainage should be attempted; otherwise, a surgical resection is chosen, and its completeness depends on the preoperative general and hearing status.

Keywords: cholesterol granuloma; computed tomography; drainage; petrous apex; surgical excision; temporal bone.

Figure 1

CT classification of cholesterol granulomas. V, fifth cranial nerve; ica, internal carotid artery; jb, jugular bulb; iac, internal auditory canal; lb, labyrinthine block; c, cochlea; eac, external auditory canal; gg, geniculate ganglion; sps, superior petrosal sinus; cg: cholesterol granuloma; blue arrows, cholesterol granuloma on the CT scans.

Figure 2

CT classification of the relationship between the cholesterol granuloma and the infracochlear, perilabyrinthine and sphenoidal air cells: ss, sigmoid sinus; sps, superior petrosal sinus; lb, labyrinthine block; fn, facial nerve; gg, geniculate ganglion; ica (or ICA), internal carotid artery; pr, promontory; jb, jugular bulb; Coch, cochlea; cg, cholesterol granuloma; *, cholesterol granuloma in the CT scan; blue arrows, possible drainage pathways.

Figure 3

Trans-sphenoidal approach. (a,b) Axial CT scan sections of a left PACG. (c) Surgical step: with a diamond bur the sphenoid sinus is opened. (d) Surgical step: with a curve dissection tool the cyst of the PACG is opened and drained. (e) Post-surgery CT scan with regular trans-sphenoidal drainage. cg, cholesterol granuloma.

Figure 4

Type B infratemporal fossa approach combined with a transotic approach. (a) Coronal CT scan of a massive right Type C PACG. (b,c) Axial T2-weighted MRI sections of the same PACG showing its hyperintense signal and its relationship with the IAC, the ICA and the clivus. (d) Surgical step: the facial nerve has been completely skeletonized from the IAC to the stylomastoid foramen and it is left in a bridge-like fashion over the surgical field; careful maneuvers are employed to dethatch the PACG from the horizontal segment of the ICA. (e) Surgical step: final surgical field where the PACG has been completely removed. cg, cholesterol granuloma; ica, internal carotid artery; fn, mastoid segment of the facial nerve; iac, internal auditory canal; fn*, intraparotid facial nerve; dgm, digastric muscle.

Figure 5

Middle cranial fossa approach. (a) Axial CT scan of a right Type C PACG with erosion of the horizontal ICA bone walls. (b,c) Axial and Coronal T1-weighted MRI sections of the same PACG, showing the typical hyperintense signal. (d) Surgical step: a craniotomy has been performed and the dura of the middle cranial fossa is carefully elevated from the skull base. (e) Surgical step: the lesion is identified after the Kawase triangle drilling. cg: cholesterol granuloma; mcf, middle fossa dura; gspn, greater superficial petrosal nerve; ae, arcuate eminence; ica, internal carotid artery.

Figure 6

Decision-making flow chart based on our CT classification of the PACG.