Letter to the Editor. Double-crescent sign and superficial subarachnoid CSF space expansion

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  • Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
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TO THE EDITOR: We read with great interest the research by Miki et al.1 (Miki K, Abe H, Morishita T, et al. Double-crescent sign as a predictor of chronic subdural hematoma recurrence following burr-hole surgery. J Neurosurg. 2019;131[6]:1905–1911). The authors indicated that the space between the dura and brain parenchyma after surgery for chronic subdural hematoma (CSDH) was sometimes longitudinally divided into two crescents, the inner crescent representing a new individual subdural hygroma, with CT density the same or similar to that of CSF, and the outer crescent showing the original hematoma cavity (Table 1). Miki et al. also reported that the new subdural hygroma indicated by the inner crescent could cause the recurrence of CSDH.

TABLE 1.

Two different interpretations for inner space in the double-crescent sign on CT after CSDH

Current StudyPrevious Studies
ReportsMiki et al., 20191Sucu & Akar, 20143
Tosaka et al., 20152
SignsDouble-crescent signDouble-layer appearance, superficial subarachnoid CSF space expansion, etc.
Outer spaceOuter original hematoma cavityOuter original hematoma cavity
Inner spaceInner new hygromaInner subarachnoid CSF space
ResultsPositive correlation to hematoma relapseNegative correlation to hematoma relapse

We previously reported the double-crescent configuration on CT after CSDH surgery in a study published 5 years ago.2 At almost the same time, Sucu and Akar also reported this sign as a “double-layer appearance.”3 We and Sucu and Akar indicated that this inner crescent (layer) represented a superficial subarachnoid CSF space, not a new hygroma (Table 1). CT may not allow reliable identification of this inner crescent as an isolated hygroma or a superficial subarachnoid space. The only way to distinguish between these entities is “the cortical vein sign” on MRI, not thickness.4 Consequently, we did not claim the occurrence of a new isolated subdural edema.

The “double-layer (crescent) sign” as described by us and Sucu and Akar did not affect the hematoma recurrence rate.2,3 We speculated that this inner crescent was associated with overnight drainage because this formation was seen shortly after drainage but was rarely seen on day 7 after surgery.2 These observations can be explained by the Monro-Kellie hypothesis,5 according to which the sum of the volumes of each intracranial element, including the brain, CSF, blood, and subdural content (in this case), remains constant. Loss of volume caused by discharge of the subdural fluid under slight negative pressure should be compensated for by expansion of the other elements. The compressed brain could expand, but brain expansion is often quite slow in the case of CSDH.6 Therefore, CSF is the most likely candidate to replace this lost volume. In other words, subarachnoid expansion may compensate for the decreased subdural volume after overnight drainage of subdural fluid.5

Miki et al.1 indicated that the double-crescent sign was positively associated with recurrence, in contrast to our findings. In my opinion, this positive association could also occur for the following reasons. Poor postoperative re-expansion of the brain parenchyma may be related to hematoma relapse. The double-crescent sign is considered to indicate poor postoperative re-expansion of the brain parenchyma, which could result in this positive relationship. Also, the postoperative double-crescent sign may very rarely include a multiloculated CSDH or new hygroma,1,7 which may cause recurrence.

However, CT is still unlikely to provide evidence that all these cavities are new isolated hygromas. In previous reports, the double-crescent sign was considered to be a combination of the expansion of the inner superficial subarachnoid CSF space and the outer original hematoma cavity.2,3 Further discussion regarding the previous findings by us and Sucu and Akar in relation to the findings reported by Miki et al. may be required.2,3

Disclosures

The author reports no conflict of interest.

References

  • 1

    Miki K, Abe H, Morishita T, Double-crescent sign as a predictor of chronic subdural hematoma recurrence following burr-hole surgery. J Neurosurg. 2019;131(6):19051911.

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  • 2

    Tosaka M, Tsushima Y, Watanabe S, Superficial subarachnoid cerebrospinal fluid space expansion after surgical drainage of chronic subdural hematoma. Acta Neurochir (Wien). 2015;157:12051214.

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  • 3

    Sucu HK, Akar Ö. Double-layer appearance after evacuation of a chronic subdural hematoma. Br J Neurosurg. 2014;28:9397.

  • 4

    McCluney KW, Yeakley JW, Fenstermacher MJ, Subdural hygroma versus atrophy on MR brain scans: “the cortical vein sign.” AJNR Am J Neuroradiol. 1992;13:13351339.

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  • 5

    Mokri B. The Monro-Kellie hypothesis: applications in CSF volume depletion. Neurology. 2001;56:17461748.

  • 6

    Kung WM, Hung KS, Chiu WT, Quantitative assessment of impaired postevacuation brain re-expansion in bilateral chronic subdural haematoma: possible mechanism of the higher recurrence rate. Injury. 2012;43: 598602.

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    • Export Citation
  • 7

    Hashimoto N, Sakakibara T, Yamamoto K, Two fluid-blood density levels in chronic subdural hematoma. Case report. J Neurosurg. 1992;77:310311.

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  • Fukuoka University Hospital and School of Medicine, Fukuoka University, Fukuoka, Japan

Response

We greatly appreciate the interest in our study expressed by Dr. Tosaka. His opinion is valuable to understanding the origin of our proposed sign, the double-crescent sign, after chronic subdural hematoma (CSDH) surgery. Although our study showed an association between the double-crescent sign and the postoperative recurrence of CSDH, the distinctive origins and mechanisms predisposing patients showing this sign to recurrence were unclear despite the fact that we suspected that the inner layer of the sign we observed (deep to the residual hematoma) constituted a new hygroma. Tosaka et al. and Sucu and Akar previously reported radiological findings similar to our sign and considered that the inner layer may have presented expansion of the subarachnoid space.1,2

As Dr. Tosaka pointed out, we examined the inner layer of the double-crescent sign using only CT scans and could not evaluate its structure in detail. Therefore, our cohort potentially included cases with the etiologies reported by Tosaka et al.1 However, in our study there were also several cases in which patients with CSDH recurrence demonstrated etiologies that could be differentiated from those hypothesized by Dr. Tosaka and his colleagues. In these patients, CT scans showed that the density of the inner layer changed and increased from that of the CSF (Fig. 1), and this phenomenon was not explained by the expansion of the subarachnoid space. Although these patients underwent burr-hole surgery for the recurrence, we did not identify any postoperative CSF leakage through the drain, which would have been observed if the recurrence was due to the expansion of the subarachnoid space.

FIG. 1.
FIG. 1.

Axial CT images of a CSDH recurrence case with our sign (double-crescent sign). A preoperative CT image (A) shows a left-lateralized CSDH. Serial CT images were obtained at postoperative days 1 (B), 6 (C), and 12 (D). Over the course of 12 days, the density of the inner layer (asterisks) deep to the residual hematoma (arrowhead) changed and increased compared with that of the CSF while the volume of the inner layer gradually increased.

The double-crescent sign may appear in cases that are heterogenous in nature. The origin of the inner layer may be elucidated via pathological analyses or further radiological examination by MRI. As Tosaka et al. explained in their article, this finding may be a passive phenomenon induced by overnight drainage and delayed brain re-expansion.1 In our series, approximately 70% of the patients with the double-crescent sign had not experienced recurrence after surgery at the time of this writing. We agree with Dr. Tosaka that the poor re-expansion of the brain after surgery may predispose patients to recurrence along with the double-crescent sign. We suspect that our sign may tend to be observed in the patients with poor brain re-expansion; however, this hypothesis remains unproven. We only investigated and observed the short-term brain re-expansion, and further examination by other methods may be required.

Contrary to our results, Tosaka et al. and Sucu and Akar reported that in their studies double-crescent–like findings were not associated with CSDH recurrence,1,2 and the recurrence rates were lower (9.7%) in the Tosaka et al. study1 than in our study (18.1%). Differences in patient characteristics, surgical procedures, and/or perioperative management may have contributed to the discrepancies in results between these studies. The significance of the double-crescent finding and its relationship with recurrence may be better understood through further research with a larger patient population and detailed imaging studies to elucidate the process of recurrence in patients showing the double-crescent sign after CSDH surgery.

References

  • 1

    Tosaka M, Tsushima Y, Watanabe S, Superficial subarachnoid cerebrospinal fluid space expansion after surgical drainage of chronic subdural hematoma. Acta Neurochir (Wien). 2015;157:12051214.

    • Search Google Scholar
    • Export Citation
  • 2

    Sucu HK, Akar Ö. Double-layer appearance after evacuation of a chronic subdural hematoma. Br J Neurosurg. 2014;28:9397.

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Contributor Notes

Correspondence Masahiko Tosaka: nstosaka@gunma-u.ac.jp.

INCLUDE WHEN CITING Published online May 8, 2020; DOI: 10.3171/2020.2.JNS20569.

Disclosures The author reports no conflict of interest.

  • View in gallery

    Axial CT images of a CSDH recurrence case with our sign (double-crescent sign). A preoperative CT image (A) shows a left-lateralized CSDH. Serial CT images were obtained at postoperative days 1 (B), 6 (C), and 12 (D). Over the course of 12 days, the density of the inner layer (asterisks) deep to the residual hematoma (arrowhead) changed and increased compared with that of the CSF while the volume of the inner layer gradually increased.

  • 1

    Miki K, Abe H, Morishita T, Double-crescent sign as a predictor of chronic subdural hematoma recurrence following burr-hole surgery. J Neurosurg. 2019;131(6):19051911.

    • Search Google Scholar
    • Export Citation
  • 2

    Tosaka M, Tsushima Y, Watanabe S, Superficial subarachnoid cerebrospinal fluid space expansion after surgical drainage of chronic subdural hematoma. Acta Neurochir (Wien). 2015;157:12051214.

    • Search Google Scholar
    • Export Citation
  • 3

    Sucu HK, Akar Ö. Double-layer appearance after evacuation of a chronic subdural hematoma. Br J Neurosurg. 2014;28:9397.

  • 4

    McCluney KW, Yeakley JW, Fenstermacher MJ, Subdural hygroma versus atrophy on MR brain scans: “the cortical vein sign.” AJNR Am J Neuroradiol. 1992;13:13351339.

    • Search Google Scholar
    • Export Citation
  • 5

    Mokri B. The Monro-Kellie hypothesis: applications in CSF volume depletion. Neurology. 2001;56:17461748.

  • 6

    Kung WM, Hung KS, Chiu WT, Quantitative assessment of impaired postevacuation brain re-expansion in bilateral chronic subdural haematoma: possible mechanism of the higher recurrence rate. Injury. 2012;43: 598602.

    • Search Google Scholar
    • Export Citation
  • 7

    Hashimoto N, Sakakibara T, Yamamoto K, Two fluid-blood density levels in chronic subdural hematoma. Case report. J Neurosurg. 1992;77:310311.

    • Search Google Scholar
    • Export Citation
  • 1

    Tosaka M, Tsushima Y, Watanabe S, Superficial subarachnoid cerebrospinal fluid space expansion after surgical drainage of chronic subdural hematoma. Acta Neurochir (Wien). 2015;157:12051214.

    • Search Google Scholar
    • Export Citation
  • 2

    Sucu HK, Akar Ö. Double-layer appearance after evacuation of a chronic subdural hematoma. Br J Neurosurg. 2014;28:9397.

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