Kopfzentrum Bielefeld

Cholesterol granuloma of the petrous apex

Colour illustration of a cross-section of the ear with an intact eardrum and a dark brown mass with golden crystal glints and a fluid level behind it

Colour illustration of an operation behind the ear: holding instruments open the approach, a bone window below the cochlea shows the dark fluid, a fine suction instrument drains it

Colour illustration of the petrous apex: skull base from the side with a semi-transparent temporal bone pyramid, at its tip a dark brown cyst with golden crystalline glints between the inner ear and the artery, below an axial section showing the cyst location

Diagnosis

A cholesterol granuloma is a slowly expanding cyst filled with cholesterol crystals in the mastoid or at the petrous apex. Under the ear microscope it appears as a dark brown to bluish shimmering area behind an intact eardrum; a hearing test can show a conductive component. Magnetic resonance imaging provides the decisive picture: the finding is bright in both sequences, which distinguishes it from other mass lesions.

Symptoms

Many granulomas are discovered incidentally on imaging. When symptoms occur, they are mostly a feeling of pressure, slow hearing loss or noises in the ear; with deeply located findings at the petrous apex, double vision or facial numbness can occur when nerves are compressed.

Causes

The granuloma forms when air cells of the petrous bone are filled with blood or inflammatory fluid and are no longer ventilated: cells break down the blood, released cholesterol crystals irritate the tissue, and a cyst filled with crystals and inflammatory cells grows slowly.

Treatment options

A small, unremarkable finding can be observed with imaging controls. Symptoms or growth indicate a draining operation: through a small bone window below the cochlea (infracochlear approach) the cyst is opened and permanently connected to the middle ear or the ear canal with a fine tube, so that the fluid does not collect again. The approach preserves hearing and the facial nerve and is reached from the ear canal.

After the procedure

The wound behind the ear usually heals within two weeks. The drainage tube remains in place permanently and is checked for patency in follow-up examinations; imaging shows that the cyst shrinks. Hearing tests document that hearing is preserved.

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