The role of exudation in chronic subdural hematomas

Chronic subdural hematomas (SDHs) are a local inflammatory process that causes the formation of a granulation tissue often referred to as the external or outer membrane. This membrane has abnormally permeable macrocapillaries. Therefore, exudation from the macrocapillaries in the outer membrane of chronic SDH may play an important role in the enlargement of chronic SDH. In this study the authors investigated the role of exudation in chronic SDH.

The authors examined 24 patients (16 men and eight women; age range 38-86 years [mean age 61.4 years]) with 27 chronic SDHs. The clinical status of the patients was evaluated according to the classification described by Markwalder. The diagnosis was established on computed tomography (CT) scans in all cases. The authors also used the Nomura Classification for judging the lesion's appearance on CT scans. Immediately after the diagnosis, all patients were administered 20 mCi (740 mBq) technetium-99m human serum albumin. Four hours later, blood and SDH samples were taken and radioactivity levels were measured in each. The ratio of activity of the samples taken from chronic SDH to the radioactivity of blood was determined as a percentage and defined as the exudation rate. On the follow-up CT scan obtained on postoperative Day 20, subdural collections thicker than 5 mm were determined to be a reaccumulation.

The correlations between the exudation rate and age of the patients, clinical grades, CT appearances, and amount of reaccumulation were investigated. In this series the average exudation rate was 13.24% (range 2.05-28.88%). The mean exudation rates according to the clinical grades assigned to patients were as follows: Grade 0, 8.67 +/- 5.64% (three patients); Grade 1, 5.07 +/- 1.43% (eight patients); Grade 2, 17.87 +/- 3.73% (seven patients); and Grade 3, 19.65 +/- 7.67% (six patients). Exudation rates in patients with Grades 2 and 3 were significantly higher than those in Grades 0 and 1 (p < 0.05). The mean exudation rates according to the lesion's appearance on CT scans were found as follows: hypodense appearance, 6.55 +/- 4.52% (eight patients); isodense appearance, 11.07 +/- 6.32% (five patients); hyperdense appearance, 19.47 +/- 13.61% (three patients); and mixed-density appearance, 17.40 +/- 5.80% (nine patients). The differences among the groups were significant (p < 0.05). The average exudation rate was statistically higher in the patients with reaccumulation (16.30 +/- 8.16%) than that in the patients without reaccumulation (9.96 +/- 6.84%) (p < 0.05).

The exudation rate in chronic SDH is correlated with a higher clinical grade (Markwalder Grade 2 or 3), mixed-density CT appearance, and reaccumulation. Therefore, exudation from macrocapillaries in the outer membrane of chronic SDH probably plays an important role in the pathophysiology and the growth of chronic SDH.