Bone Caries (in otology)

Bone caries in otology (from Latin caries, meaning decay) is a historical term used in otorhinolaryngology to describe a process of slow, chronic suppurative–necrotizing inflammation of bone tissue involving the temporal bone and the auditory ossicles.

In modern medical terminology, this condition is more accurately defined as chronic osteitis or osteomyelitis. The process is characterized by progressive destruction and breakdown of bone as a result of prolonged inflammation. Cholesteatoma is the most common cause of bone caries in the middle ear.

Aetiology and Pathophysiology

Bone destruction in chronic otitis media is a multifactorial process driven by the prolonged effects of infection and pressure on bony structures.

Main Causes and Mechanisms:

• Cholesteatoma: The primary cause. The cholesteatoma matrix produces aggressive enzymes (collagenases, proteases) that directly dissolve bone. In addition, the expanding cholesteatoma exerts pressure on the bony walls, impairing their blood supply (ischemia) and causing bone resorption.
• Chronic suppurative otitis media (without cholesteatoma): Long-standing granulation tissue and polyps, as well as purulent exudate, can impair bone nutrition and lead to gradual bone erosion.
• Specific infections: Tuberculosis or syphilis of the ear (rare).
• Malignant neoplasms: Middle ear cancer.

The auditory ossicles are most vulnerable to the carious process, particularly the long process of the incus, due to its delicate anatomy and poor blood supply. The walls of the attic (epitympanum) and the structures of the mastoid process are also frequently affected.

Clinical significance

The clinical manifestations of bone caries correspond to the symptoms of the underlying disease that caused it (most commonly chronic epitympanitis with cholesteatoma).

Main symptoms:

• Persistent or intermittent purulent otorrhea, often with a strong, foul, putrid smell.
• Progressive hearing loss, typically conductive or mixed, resulting from destruction of the tympanic membrane and the ossicular chain.
• Signs of complications (with extension of the destructive process): Vertigo (due to formation of a labyrinthine fistula), facial nerve paresis (due to erosion of the facial nerve canal wall), and headache.

The gold standard for diagnosing osseous destruction of the ear is computed tomography (CT) of the temporal bones. CT imaging allows for detailed assessment of the auditory ossicles, the walls of the tympanic cavity, and the mastoid process, enables detection of the presence and extent of cholesteatoma, and helps in surgical planning.

Bone caries is always treated surgically. It involves performing a sanitation middle ear surgery, aimed at the complete removal of pathological tissues (cholesteatoma, granulation tissue) and all necrotic bone segments.

Differential Diagnosis

The primary diagnostic goal is to determine the underlying cause of bone destruction. Cholesteatoma appears on CT as a soft tissue mass causing clearly defined bone erosion. It should be differentiated from a malignant tumor, which typically demonstrates more aggressive, infiltrative growth with irregular margins of bone destruction. Chronic otitis media with granulation and without cholesteatoma usually causes less pronounced, pitted bone erosion. The final diagnosis is often established intraoperatively and confirmed by histological examination of the excised tissues.