Posterior fossa arachnoiditis

For a cyst formed by thickened arachnoid in the cerebellomedullary cistern, many different terms have been used, such as “arachnoid cyst of the cerebellomedullary cistern”, “cystic hydrops of the posterior fossa” or “inferior midline cyst” ¹⁾.

In 1889, Maunsell ²⁾ first reported an arachnoid cyst in the posterior fossa. In 1932, Craig ³⁾ reported chronic cystic arachnoiditis described the clinical manifestations and ascribed the disease to an inflammatory reaction of the arachnoid. In 1958 and 1959, Ogleznev ⁴⁾ and Laponogov ⁵⁾ reported their experience with the surgical treatment of this disease. Later, the clinical features, pathogenesis, and treatment of the condition occasionally were described, but large collections of patients were reported rarely ^{6) 7) 8)}

Chronic arachnoiditis in the posterior fossa is not rare, particularly in northern China. Most of the patients are young and very few are over the age of 50 years ⁹⁾.

Symptomatic arachnoiditis after posterior fossa neurosurgical procedures such as decompression of Chiari malformation is a possible complication.

Clinical presentation is generally insidious and delayed by months or years. It causes disturbances in the normal flow of cerebrospinal fluid and enlargement of a syrinx cavity in the upper spinal cord.

The illness is with long intermissions between relapses which are finally recognized as due to “increased intracranial pressure”.

Posterior fossa arachnoiditis treatment.

The outcome of correct management is usually satisfactory.

Between 1970 and September 1981, 82 patients with chronic arachnoiditis in the posterior fossa were admitted to this department. All the cases were confirmed by operation and, in most cases, by histological examination of the removed tissue. These patients constituted 0.94% of 8708 neurosurgical cases admitted during the same period. They also constituted 22.84% of 359 who had posterior fossa operations with increased intracranial pressure ¹⁰⁾.