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Does the Mount Fuji Sign always signify ‘tension’ pneumocephalus? An exception and a reappraisal
European Journal of Radiology Extra 78 (2011) e5–e7
Contents lists available at ScienceDirect
European Journal of Radiology Extra journal homepage: intl.elsevierhealth.com/journals/ejrex
Does the Mount Fuji Sign always signify ‘tension’ pneumocephalus? An exception and a reappraisal Sandeep G. Jakhere a,∗ , Deepak A. Yadav a , Darshan G. Jain a , Srikant Balasubramaniam b a b
Department of Radiology, B Y L Nair Charitable Hospital and T N Medical College, Mumbai Central, Mumbai, Maharashtra, India 400008 Department of Neurosurgery, B Y L Nair Charitable Hospital and T N Medical College, Mumbai Central, Mumbai, Maharashtra, India 400008
a r t i c l e
i n f o
Article history: Received 27 November 2010 Received in revised form 6 January 2011 Accepted 17 January 2011
Keywords: Pneumocephalus Mount Fuji Sign
a b s t r a c t Pneumocephalus is expected after any craniotomy and usually resolves without any sequelae. However if the air entering the cranial cavity gets entrapped, it can lead to tension pneumocephalus and can have disastrous consequences. It is of utmost clinical importance to differentiate a tension pneumocephalus from a non-tension pneumocephalus as the latter does not usually require decompressive surgery. CT scan is considered the gold standard and diagnostic modality of choice for the diagnosis of pneumocephalus in the post-operative period. The Peaking sign and Mount Fuji sign are proposed as fairly specific for tension pneumocephalus, the latter being the most specific and an important sign to differentiate it from nontension pneumocephalus. We present a case of a 20 year old male whose post-operative CT brain showed the typical Mount Fuji sign suggestive of tension pneumocephalus but was managed conservatively without any decompressive surgery. © 2011 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Mount Fuji is the tallest volcanic peak in Japan standing at a height of 3776 meters and has erupted at least 17 times since 781 AD, the most recent eruption occurring in 1707 [1,2]. This iconic geographical landmark has inspired the Mount Fuji sign in Radiology which is considered synonymous with tension pneumocephalus. Ishiwata et al. [3] proposed this sign in 1988 when they found this typical sign in four of five cases with subdural tension pneumocephalus, but it was not seen in any patient with non-tension pneumocephalus. Since then many reports have been published in which the Mount Fuji sign has been corroborated with tension pneumocephalus [4–6] and it was proposed as an important differentiating point between tension pneumocephalus and non-tension pneumocephalus. Tension pneumocephalus is usually a surgical emergency unlike non-tension pneumocephalus which can be managed conservatively. Shaikh et al. [6] reviewed 30 cases of tension pneumocephalus reported till date occurring after burrhole surgery for chronic subdural hematoma evacuation and all the patients had to undergo emergency decompression to reduce the increased subdural pressure due to tension pneumocephalus.
∗ Corresponding author at: 2/13 Government Colony, Near Lala Lajpatrai College, Haji Ali, Mumbai, Maharashtra, India 400034. Tel.: +91 9920469297. E-mail addresses: [email protected] (S.G. Jakhere), [email protected] (D.A. Yadav), [email protected] (D.G. Jain), [email protected] (Srikant Balasubramaniam). 1571-4675/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejrex.2011.01.002
We present a case of a 20 year old male whose post-operative CT brain showed the typical Mount Fuji sign suggestive of tension pneumocephalus but showed no neurological deterioration and was managed conservatively without any decompressive surgery.
2. Case report A 20 year old male was operated in the Neurosurgery department for a large arachnoid cyst in the left parietal region. A left posterior parietal craniotomy was performed followed by fenestration of the cyst wall and communication of the cyst with the left lateral ventricle. A ventriculo-peritoneal shunt was placed partly in the fenestrated arachnoid cyst and partly within the frontal horn of left lateral ventricle. The post-operative period was uneventful except for an episode of visual hallucinations on the second post operative day which lasted for 24 h. On the fourth post operative day, CT brain was done to check the position of the VP shunt. CT brain revealed pneumoventricle and extensive subdural pneumocephalus overlying bilateral frontal lobes causing compression of the frontal lobes and separation of their tips characteristic of the Mount Fuji Sign (Figs. 1 and 2). The VP shunt was noted in situ and there was no hydrocephalus. As the patient did not have any clinical symptoms suggestive of tension pneumocephalus, he was managed conservatively and a repeat CT scan done after 4 days revealed near complete resolution (Figs. 3 and 4).
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S.G. Jakhere et al. / European Journal of Radiology Extra 78 (2011) e5–e7
Fig. 1. Lateral skull topogram showing pneumocephalus (thin arrow) and VP shunt (thick arrow).
3. Discussion Pneumocephalus is defined as air located within the cranial cavity due to a pathological communication with the ambient air [7]. The first description of a pneumocephalus was provided by Thomas in 1866 during the autopsy of a patient who suffered trauma [8]. Pneumocephalus was diagnosed on plain skull radiographs by Luckett in 1913 [9] but the term pneumocephalus was coined and first used by Wolff in 1914 [10]. Post operative pneumocephalus was first reported by Markham in 1967 [11].
Fig. 2. Axial CT brain showing pneumocephalus causing compression of bilateral frontal lobes with separation of their tips and resultant twin peaks (arrows) signifying Mount Fuji Sign.
Fig. 3. Follow up lateral skull topogram after 4 days showing near complete resolution of pneumocephalus.
Pneumocephalus is expected after craniotomy because there is a breach in the dura and as the CSF leaks out, air gets sucked in to replace the CSF volume. More space is created for the air to be sucked in as the brain volume shrinks due to hyperventilation, steroid and diuretics. After the dura is closed few air locules may remain inside and are usually of no clinical significance. It usually resolves with rehydration, normalization of CO2 level, N2 O resorption and replacement of the CSF [12]. The incidence of pneumocephalus decreases in the 1st, 2nd and 3rd post operative week to 75%, 60% and 26% respectively [13]. Tension pneumocephalus occurs when the air entering the cranial cavity gets trapped causing sig-
Fig. 4. Follow up axial CT brain after 4 days showing near complete resolution of the pneumocephalus.
S.G. Jakhere et al. / European Journal of Radiology Extra 78 (2011) e5–e7
nificant compression of the brain resulting in neurological changes. It is commonly observed after evacuation of sub dural hematoma with an incidence of 2.5–16% [14]. As little as 25 ml of air is sufficient to cause tension pneumocephalus [15]. Two specific signs have been proposed for the diagnosis of subdural pneumocephalus on CT brain: (1) Peaking Sign; (2) Mount Fuji Sign. Peaking sign is characterized by large collection of air over the anterior and lateral portion of bilateral frontal lobes causing its compression. The air does not cause any separation of the tips of the frontal lobe, thereby leading to an appearance of a single peak in the midline. Pop et al. thought that the peak was formed by bridging veins entering the superior sagittal sinus [16]. Ishiwata et al. found this sign in one patient with non-tension pneumocephalus but did not find it in any of the patients with tension pneumocephalus. Mount Fuji sign is characterized by large air collections over bilateral frontal lobes which cause compression of frontal lobes and separation of the tips of the frontal lobes typically forming twin peaks. The characteristic separation of the tips of the frontal lobes indicates that the tension of the air exceeds the surface tension of the CSF between the frontal lobes. A CT scan of brain is considered the most accurate method and a gold standard for the diagnosis of tension pneumocephalus (which is considered as surgical emergency) and to differentiate it from relatively benign non-tension pneumocephalus which is not of much clinical significance. Ishiwata et al. concluded that the Mount Fuji sign is suggestive of higher subdural pressure than the peaking sign does, although the absence of Mount Fuji sign does not necessarily rule out subdural tension pneumocephalus. Even partial replacement of fluid by air may cause neurological deterioration because the vulnerability of the brain to subdural air is quite variable from patient to patient and may actually involve more complex mechanisms rather than just physical compression. Some authors have concurred with the findings of Ishiwata et al. and concluded that Mount Fuji sign indeed indicates more severe pneumocephalus than the peaking sign and the necessity of emergent decompression [17]. The commonly proposed hypotheses for the development of tension pneumocephalus are [18] (1) Inverted soda bottle phenomenon: Due to the continuous leakage of CSF either through a VP shunt or CSF fistula, a negative intracranial pressure is generated thereby slowing replacement of the lost fluid by air which seeps in through small dural defects. (2) Ball valve mechanism: According to this hypothesis air enters the intracranial cavity through a defect whenever the extra cranial pressure exceeds the intra cranial pressure (e.g. while sneezing or coughing). After the air has entered the intracranial cavity, the raised intracranial pressure forces the brain parenchyma under pressure to block the entry site. Thereby effectively trapping the intra cranial air. Repeated bouts of coughing and sneezing over a period of time can lead to relatively large accumulations of air. A third mechanism has been proposed to explain tension pneumocephalus development in the intra operative period. If nitrous oxide is used for anesthesia during surgery on a patient with a small pneumocephalus, the nitrous oxide will diffuse into the air filled cavity 34 times faster than nitrogen diffuses out. Thus the
e7
volume of pneumocephalus may rise rapidly resulting in tension pneumocephalus. Our case report is unique due to the fact that although the post-operative CT brain showed the typical Mount Fuji sign with compression and characteristic separation of tips of the frontal lobes, the patient was clinically stable and showed no neurological deterioration. Patient was managed conservatively and there was complete resolution of the pneumocephalus in the follow up CT after 3 days. We propose that Mount Fuji sign does not always signify tension pneumocephalus and may be seen in a few subsets of patients with non-tension pneumocephalus. Other complex mechanisms rather than just physical compression of frontal lobes may be responsible for the clinical symptoms and require further elucidation. Conflicts of interest None Acknowledgements We would like to acknowledge Dr. Vipul Chemburkar, Dr. Bhakti Yeragi and Dr. Devendra K. Tyagi for reviewing the article for its content and accuracy. References [1] Suzuki Y, Fujii T. Effect of syneruptive decompression path on shifting intensity in basaltic sub-Plinian eruption: implication of microlites in Yufune-2 scoria from Fuji volcano, Japan. J Volcanol Geotherm Res 2010;198(1–2):158–76. [2] Aizawa K, Yoshimura R, Oshiman N, et al. Hydrothermal system beneath Mt, Fuji volcano inferred from magnetotellurics and electric self-potential. Earth Planet Sci Lett 2005;235:343–55. [3] Ishiwata Y, Fujitsu K, Sekino T, et al. Subdural tension pneumocephalus following surgery for chronic subdural hematoma. J Neurosurg 1988;68:58–61. [4] Vanhoenacker FM, Herz R, Vandervliet EJ, Parizel PM. The Mount Fuji sign in tension pneumocephalus. JBR-BTR 2008;91:175. [5] Michel SJ. The Mount Fuji Sign. Radiology 2004;232:449–50. [6] Shaikh N, Ummunnisa F, Masood I, Hanssens Y. Tension pneumocephalus as complication of burr-hole drainage of chronic subdural hematoma: a case report. Surg Neurol Int 2010;1:27. [7] Eltorai IM, Montroy RE, Kaplan SL, et al. Pneumocephalus secondary to cerebrospinal fluid leak associated with a lumbar pressure ulcer in a man with paraplegia. J Spinal Cord Med 2003;26:262–9. [8] Thomas L. Du Pneumatocele du crane. Arch Gen Med (Paris) 1866;1:34–55. [9] Luckett WH. Air in the ventricles of the brain following a fracture of the skull: report of a case. Surg Gynecol Obstet 1913;17:237–40. [10] Wolff E. Luftansammlung im rechten Seitenventrikel des Gehirns (Pneumozephalus). Munch Med Wochenschr 1914;61:899. [11] Markham JW. The clinical features of pneumocephalus based on a survey of 284 cases with report of 11 additional cases. Acta Neurochir 1967;16:1–78. [12] Clevens RA, Marentette LJ, Esclamado RM, Wolf GT, Ross DA. Incidence and management of tension pneumocephalus after anterior craniofacial resection: case reports and review of the literature. Otolaryngol Head Neck Surg 1999;120:579–83. [13] Reasoner DK, Todd MM, Scamman FL, Warner DS. The incidence of pneumocephalus after supratentorial craniotomy. Observations on the disappearance of intracranial air. Anesthesiology 1994;80(5):1008–12. [14] Thapa A, Agrawal B. Mount Fuji Sign in tension pneumocephalus. Indian J Neurotrauma 2009;6(2):161–2. [15] Aoki N, Sakai T. Computed tomography feature immediately after replacement of haematoma with oxygen through percutaneous subdural tapping for the treatment of chronic subdural haematoma in adults. Acta Neurochir (Wein) 1993;20:44–6. [16] Pop PM, Thompson JR, Zeinke DE, et al. Tension pneumocephalus. J Comput Assist Tomogr 1982;6:894–901. [17] Yamashita S, Tsuchimochi W, Yonekawa T, Kyoraku I, Shiomi K, Nakazato M. The Mount Fuji Sign on MRI. Intern Med 2009;48:1567–8. [18] Hong W, Yoo C, Park C, Lee S. Two cases of delayed tension pneumocephalus. J Korean Neurosurg Soc 2005;37:59–62.
Contents lists available at ScienceDirect
European Journal of Radiology Extra journal homepage: intl.elsevierhealth.com/journals/ejrex
Does the Mount Fuji Sign always signify ‘tension’ pneumocephalus? An exception and a reappraisal Sandeep G. Jakhere a,∗ , Deepak A. Yadav a , Darshan G. Jain a , Srikant Balasubramaniam b a b
Department of Radiology, B Y L Nair Charitable Hospital and T N Medical College, Mumbai Central, Mumbai, Maharashtra, India 400008 Department of Neurosurgery, B Y L Nair Charitable Hospital and T N Medical College, Mumbai Central, Mumbai, Maharashtra, India 400008
a r t i c l e
i n f o
Article history: Received 27 November 2010 Received in revised form 6 January 2011 Accepted 17 January 2011
Keywords: Pneumocephalus Mount Fuji Sign
a b s t r a c t Pneumocephalus is expected after any craniotomy and usually resolves without any sequelae. However if the air entering the cranial cavity gets entrapped, it can lead to tension pneumocephalus and can have disastrous consequences. It is of utmost clinical importance to differentiate a tension pneumocephalus from a non-tension pneumocephalus as the latter does not usually require decompressive surgery. CT scan is considered the gold standard and diagnostic modality of choice for the diagnosis of pneumocephalus in the post-operative period. The Peaking sign and Mount Fuji sign are proposed as fairly specific for tension pneumocephalus, the latter being the most specific and an important sign to differentiate it from nontension pneumocephalus. We present a case of a 20 year old male whose post-operative CT brain showed the typical Mount Fuji sign suggestive of tension pneumocephalus but was managed conservatively without any decompressive surgery. © 2011 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Mount Fuji is the tallest volcanic peak in Japan standing at a height of 3776 meters and has erupted at least 17 times since 781 AD, the most recent eruption occurring in 1707 [1,2]. This iconic geographical landmark has inspired the Mount Fuji sign in Radiology which is considered synonymous with tension pneumocephalus. Ishiwata et al. [3] proposed this sign in 1988 when they found this typical sign in four of five cases with subdural tension pneumocephalus, but it was not seen in any patient with non-tension pneumocephalus. Since then many reports have been published in which the Mount Fuji sign has been corroborated with tension pneumocephalus [4–6] and it was proposed as an important differentiating point between tension pneumocephalus and non-tension pneumocephalus. Tension pneumocephalus is usually a surgical emergency unlike non-tension pneumocephalus which can be managed conservatively. Shaikh et al. [6] reviewed 30 cases of tension pneumocephalus reported till date occurring after burrhole surgery for chronic subdural hematoma evacuation and all the patients had to undergo emergency decompression to reduce the increased subdural pressure due to tension pneumocephalus.
∗ Corresponding author at: 2/13 Government Colony, Near Lala Lajpatrai College, Haji Ali, Mumbai, Maharashtra, India 400034. Tel.: +91 9920469297. E-mail addresses: [email protected] (S.G. Jakhere), [email protected] (D.A. Yadav), [email protected] (D.G. Jain), [email protected] (Srikant Balasubramaniam). 1571-4675/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejrex.2011.01.002
We present a case of a 20 year old male whose post-operative CT brain showed the typical Mount Fuji sign suggestive of tension pneumocephalus but showed no neurological deterioration and was managed conservatively without any decompressive surgery.
2. Case report A 20 year old male was operated in the Neurosurgery department for a large arachnoid cyst in the left parietal region. A left posterior parietal craniotomy was performed followed by fenestration of the cyst wall and communication of the cyst with the left lateral ventricle. A ventriculo-peritoneal shunt was placed partly in the fenestrated arachnoid cyst and partly within the frontal horn of left lateral ventricle. The post-operative period was uneventful except for an episode of visual hallucinations on the second post operative day which lasted for 24 h. On the fourth post operative day, CT brain was done to check the position of the VP shunt. CT brain revealed pneumoventricle and extensive subdural pneumocephalus overlying bilateral frontal lobes causing compression of the frontal lobes and separation of their tips characteristic of the Mount Fuji Sign (Figs. 1 and 2). The VP shunt was noted in situ and there was no hydrocephalus. As the patient did not have any clinical symptoms suggestive of tension pneumocephalus, he was managed conservatively and a repeat CT scan done after 4 days revealed near complete resolution (Figs. 3 and 4).
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S.G. Jakhere et al. / European Journal of Radiology Extra 78 (2011) e5–e7
Fig. 1. Lateral skull topogram showing pneumocephalus (thin arrow) and VP shunt (thick arrow).
3. Discussion Pneumocephalus is defined as air located within the cranial cavity due to a pathological communication with the ambient air [7]. The first description of a pneumocephalus was provided by Thomas in 1866 during the autopsy of a patient who suffered trauma [8]. Pneumocephalus was diagnosed on plain skull radiographs by Luckett in 1913 [9] but the term pneumocephalus was coined and first used by Wolff in 1914 [10]. Post operative pneumocephalus was first reported by Markham in 1967 [11].
Fig. 2. Axial CT brain showing pneumocephalus causing compression of bilateral frontal lobes with separation of their tips and resultant twin peaks (arrows) signifying Mount Fuji Sign.
Fig. 3. Follow up lateral skull topogram after 4 days showing near complete resolution of pneumocephalus.
Pneumocephalus is expected after craniotomy because there is a breach in the dura and as the CSF leaks out, air gets sucked in to replace the CSF volume. More space is created for the air to be sucked in as the brain volume shrinks due to hyperventilation, steroid and diuretics. After the dura is closed few air locules may remain inside and are usually of no clinical significance. It usually resolves with rehydration, normalization of CO2 level, N2 O resorption and replacement of the CSF [12]. The incidence of pneumocephalus decreases in the 1st, 2nd and 3rd post operative week to 75%, 60% and 26% respectively [13]. Tension pneumocephalus occurs when the air entering the cranial cavity gets trapped causing sig-
Fig. 4. Follow up axial CT brain after 4 days showing near complete resolution of the pneumocephalus.
S.G. Jakhere et al. / European Journal of Radiology Extra 78 (2011) e5–e7
nificant compression of the brain resulting in neurological changes. It is commonly observed after evacuation of sub dural hematoma with an incidence of 2.5–16% [14]. As little as 25 ml of air is sufficient to cause tension pneumocephalus [15]. Two specific signs have been proposed for the diagnosis of subdural pneumocephalus on CT brain: (1) Peaking Sign; (2) Mount Fuji Sign. Peaking sign is characterized by large collection of air over the anterior and lateral portion of bilateral frontal lobes causing its compression. The air does not cause any separation of the tips of the frontal lobe, thereby leading to an appearance of a single peak in the midline. Pop et al. thought that the peak was formed by bridging veins entering the superior sagittal sinus [16]. Ishiwata et al. found this sign in one patient with non-tension pneumocephalus but did not find it in any of the patients with tension pneumocephalus. Mount Fuji sign is characterized by large air collections over bilateral frontal lobes which cause compression of frontal lobes and separation of the tips of the frontal lobes typically forming twin peaks. The characteristic separation of the tips of the frontal lobes indicates that the tension of the air exceeds the surface tension of the CSF between the frontal lobes. A CT scan of brain is considered the most accurate method and a gold standard for the diagnosis of tension pneumocephalus (which is considered as surgical emergency) and to differentiate it from relatively benign non-tension pneumocephalus which is not of much clinical significance. Ishiwata et al. concluded that the Mount Fuji sign is suggestive of higher subdural pressure than the peaking sign does, although the absence of Mount Fuji sign does not necessarily rule out subdural tension pneumocephalus. Even partial replacement of fluid by air may cause neurological deterioration because the vulnerability of the brain to subdural air is quite variable from patient to patient and may actually involve more complex mechanisms rather than just physical compression. Some authors have concurred with the findings of Ishiwata et al. and concluded that Mount Fuji sign indeed indicates more severe pneumocephalus than the peaking sign and the necessity of emergent decompression [17]. The commonly proposed hypotheses for the development of tension pneumocephalus are [18] (1) Inverted soda bottle phenomenon: Due to the continuous leakage of CSF either through a VP shunt or CSF fistula, a negative intracranial pressure is generated thereby slowing replacement of the lost fluid by air which seeps in through small dural defects. (2) Ball valve mechanism: According to this hypothesis air enters the intracranial cavity through a defect whenever the extra cranial pressure exceeds the intra cranial pressure (e.g. while sneezing or coughing). After the air has entered the intracranial cavity, the raised intracranial pressure forces the brain parenchyma under pressure to block the entry site. Thereby effectively trapping the intra cranial air. Repeated bouts of coughing and sneezing over a period of time can lead to relatively large accumulations of air. A third mechanism has been proposed to explain tension pneumocephalus development in the intra operative period. If nitrous oxide is used for anesthesia during surgery on a patient with a small pneumocephalus, the nitrous oxide will diffuse into the air filled cavity 34 times faster than nitrogen diffuses out. Thus the
e7
volume of pneumocephalus may rise rapidly resulting in tension pneumocephalus. Our case report is unique due to the fact that although the post-operative CT brain showed the typical Mount Fuji sign with compression and characteristic separation of tips of the frontal lobes, the patient was clinically stable and showed no neurological deterioration. Patient was managed conservatively and there was complete resolution of the pneumocephalus in the follow up CT after 3 days. We propose that Mount Fuji sign does not always signify tension pneumocephalus and may be seen in a few subsets of patients with non-tension pneumocephalus. Other complex mechanisms rather than just physical compression of frontal lobes may be responsible for the clinical symptoms and require further elucidation. Conflicts of interest None Acknowledgements We would like to acknowledge Dr. Vipul Chemburkar, Dr. Bhakti Yeragi and Dr. Devendra K. Tyagi for reviewing the article for its content and accuracy. References [1] Suzuki Y, Fujii T. Effect of syneruptive decompression path on shifting intensity in basaltic sub-Plinian eruption: implication of microlites in Yufune-2 scoria from Fuji volcano, Japan. J Volcanol Geotherm Res 2010;198(1–2):158–76. [2] Aizawa K, Yoshimura R, Oshiman N, et al. Hydrothermal system beneath Mt, Fuji volcano inferred from magnetotellurics and electric self-potential. Earth Planet Sci Lett 2005;235:343–55. [3] Ishiwata Y, Fujitsu K, Sekino T, et al. Subdural tension pneumocephalus following surgery for chronic subdural hematoma. J Neurosurg 1988;68:58–61. [4] Vanhoenacker FM, Herz R, Vandervliet EJ, Parizel PM. The Mount Fuji sign in tension pneumocephalus. JBR-BTR 2008;91:175. [5] Michel SJ. The Mount Fuji Sign. Radiology 2004;232:449–50. [6] Shaikh N, Ummunnisa F, Masood I, Hanssens Y. Tension pneumocephalus as complication of burr-hole drainage of chronic subdural hematoma: a case report. Surg Neurol Int 2010;1:27. [7] Eltorai IM, Montroy RE, Kaplan SL, et al. Pneumocephalus secondary to cerebrospinal fluid leak associated with a lumbar pressure ulcer in a man with paraplegia. J Spinal Cord Med 2003;26:262–9. [8] Thomas L. Du Pneumatocele du crane. Arch Gen Med (Paris) 1866;1:34–55. [9] Luckett WH. Air in the ventricles of the brain following a fracture of the skull: report of a case. Surg Gynecol Obstet 1913;17:237–40. [10] Wolff E. Luftansammlung im rechten Seitenventrikel des Gehirns (Pneumozephalus). Munch Med Wochenschr 1914;61:899. [11] Markham JW. The clinical features of pneumocephalus based on a survey of 284 cases with report of 11 additional cases. Acta Neurochir 1967;16:1–78. [12] Clevens RA, Marentette LJ, Esclamado RM, Wolf GT, Ross DA. Incidence and management of tension pneumocephalus after anterior craniofacial resection: case reports and review of the literature. Otolaryngol Head Neck Surg 1999;120:579–83. [13] Reasoner DK, Todd MM, Scamman FL, Warner DS. The incidence of pneumocephalus after supratentorial craniotomy. Observations on the disappearance of intracranial air. Anesthesiology 1994;80(5):1008–12. [14] Thapa A, Agrawal B. Mount Fuji Sign in tension pneumocephalus. Indian J Neurotrauma 2009;6(2):161–2. [15] Aoki N, Sakai T. Computed tomography feature immediately after replacement of haematoma with oxygen through percutaneous subdural tapping for the treatment of chronic subdural haematoma in adults. Acta Neurochir (Wein) 1993;20:44–6. [16] Pop PM, Thompson JR, Zeinke DE, et al. Tension pneumocephalus. J Comput Assist Tomogr 1982;6:894–901. [17] Yamashita S, Tsuchimochi W, Yonekawa T, Kyoraku I, Shiomi K, Nakazato M. The Mount Fuji Sign on MRI. Intern Med 2009;48:1567–8. [18] Hong W, Yoo C, Park C, Lee S. Two cases of delayed tension pneumocephalus. J Korean Neurosurg Soc 2005;37:59–62.