Importance of Frontal Horn Ratio and Optimal CSF Drainage in the Treatment of Very Low-Pressure Hydrocephalus

Abstract

Introduction Unlike low-pressure hydrocephalus, very low pressure hydrocephalus (VLPH) is a rarely reported clinical entity previously described to be associated with poor outcomes and to be possibly refractory to treatment with continued cerebrospinal fluid (CSF) drainage at subatmospheric pressures. ^{1, 2} We present four cases of VLPH following resection of suprasellar lesions and hypothesize that untreatable patients can be identified early, thereby avoiding futile prolonged external ventricular drainage in ICU. Methods We performed a retrospective chart review of four cases of VLPH encountered between 2007 and 2015 in two different institutions and practices and tried to identify factors contributing to successful treatment. We hypothesized that normalization of frontal horn ratio (FHR), optimization of volume of CSF drained, and avoidance of fluid shifts would contribute to improved Glasgow Coma Score (GCS). We examined fluid shifts by studying net fluids shifts and serum levels of sodium, urea, and creatinine. We used Pearson and Spearman correlations to identify measures that would correlate with improved GCS. Results Our study reveals that improving GCS is positively correlated with decreased FHR and increased CSF drainage within an optimal range. The most important determinant of good outcome is retention of brain viscoelasticity as evidenced by restoration and maintenance of good GCS score despite fluctuations in FHR. Conclusion Futile prolonged subatmospheric drainage can be avoided by declining to continue treatment in patients who have permanently altered brain compliance secondary to unsealed CSF leaks, irremediable ventriculitis, and who are therefore unable to sustain an improved neurologic examination.

Keywords: CSF leak; anterior skull base surgery; frontal horn ratio; suprasellar lesions; transsphenoidal surgery; very low pressure hydrocephalus (VLPH).

Fig. 1

Patient 2, recurrent macroadenoma: ( A ) T1W coronal brain MRI with gadolinium. ( B ) T1W sagittal brain MRI with gadolinium, and ( C ) T2-weighted (T2W) axial brain magnetic resonance imaging (MRI). (Preadmission), GCS: 15, FHR: 0.38. Abbreviations: FHR, frontal horn ratio; GCS, Glasgow Coma Score; MRI, magnetic resonance imaging. The images reflect the situation on the admission day indicated in parentheses.

Fig. 2

Patient 2, noncontrast axial brain CT scan: Recurrent pneumocephalus. Reparation of CSF leak and EVD removed on Day #33. (Day #31) Average GCS: 12.75, FHR: 0.42, ICP: >10, EVD set to drain at 10 cmH ₂ O, doesn't drain. Abbreviations: CSF, cerebrospinal fluid; CT, computed tomography; EVD, external ventricular drain; FHR, frontal horn ratio; ICP, intracranial pressure.

Fig. 3

Patient 2, noncontrast axial brain CT scan: (Day #88) Average GCS: 12.57, FHR: 0.35, negative pressure drainage stopped on Day #84, EVD set. Inadequate negative pressure drainage. Abbreviations: CT, computed tomography; FHR, frontal horn ratio; EVD, external ventricular drain; GCS, Glasgow Coma Score.

Fig. 4

Patient 2, noncontrast axial brain CT scan: Hydrocephalus worsens: (Day #97) Average GCS: 11.75, FHR: 0.54, ICP: 0–5, EVD set to drain at 0 mmHg. Abbreviations: CT, computed tomography; FHR, frontal horn ratio; EVD, external ventricular drain; GCS, Glasgow Coma Score.

Fig. 5

Patient 2, noncontrast axial brain CT scan: Before death, (Day #108) Average GCS: 9.4, FHR: 0.47, ICP: <5, EVD set to drain at 5 cmH ₂ O. Care was withdrawn on Day #121, after futile low pressure drainage. Autopsy revealed persistent pus in surgical site despite antibiotics. Abbreviations: CT, computed tomography; FHR, frontal horn ratio; EVD, external ventricular drain; GCS, Glasgow Coma Score; ICP, intracranial pressure.

Fig. 6

Patient 3, Preadmission baseline macroadenoma axial T2-weighted MRI, GCS = 15, FHR: 0.34. Abbreviations: MRI, magnetic resonance imaging; FHR, frontal horn ratio; GCS, Glasgow Coma Score.

Fig. 7

Patient 3, noncontrast axial brain CT scan: Had CSF leak repair and lumbar drain insertion on Day #22. (Day #52), Decreased level of consciousness, needs stimulation, periventricular edema around lateral ventricle horns, GCS: 10, FHR: 0.42, Lumbar drain set to drain at -12.5 cmH ₂ O. VP shunt day: 59. Shunt revision day: 65. Abbreviations: CSF, cerebrospinal fluid; CT, computed tomography; FHR, frontal horn ratio; GCS, Glasgow Coma Score.

Fig. 8

Patient 3, noncontrast axial brain CT scan: (Day #75) Shunt failure, average GCS: 12.57, FHR: 0.46, EVD set to drain at –5 cmH ₂ O.

Fig. 9

Patient 3, noncontrast axial brain CT scan: FHR stays closer to baseline until Day #123 (Day #123) GCS: 15, FHR: 0.4, EVD set to drain at –1 cmH ₂ O. Prolonged weaning of subatmospheric drainage of CSF over 15 weeks to 5 cmH ₂ O. Trial of external ventricular drainage with valve for 7 days. VP shunt on day #189, Strata valve set to 0.5, FHR: 0.41 at discharge scan. Abbreviations: CSF, cerebrospinal fluid; CT, computed tomography; EVD, external ventricular drain; FHR, frontal horn ratio; GCS, Glasgow Coma Score.

Fig. 10

Most recent follow-up T2-weighted axial brain MRI: 2.5 years after VP shunt. Strata valve set at 0.5. GCS: 15, FHR 0.35. Abbreviations: FHR, frontal horn ratio; GCS, Glasgow Coma Score; MRI, magnetic resonance imaging.

Fig. 11

Evaluation of brain compliance, calculated by: Response to treatment is not limited by variability in FHR. The vertical lines show the range in which the patients' FHR can vary while maintaining a GCS of 15. The X on each line represents each patients' baseline FHR. Poor compliance predisposes the patient to unsuccessful treatment. Patient 1 had an irreversibly floppy brain. Patient 2 had an abnormally stiff brain. Patient 3 had regained almost normal brain compliance. Patient 4 had regained his baseline brain stiffness. Abbreviations: FHR, frontal horn ratio; GCS, Glasgow Coma Score.