C M Chan

Queen Elizabeth Hospital, Hong Kong, Hong Kong

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Publications (19)31.36 Total impact

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    ABSTRACT: OBJECTIVES. To evaluate the efficacy and complications of endovascular treatment for ruptured internal carotid artery pseudoaneurysms following irradiation of nasopharyngeal carcinoma. DESIGN. Retrospective case series. SETTING. Tertiary neurosurgical referral unit of a Hong Kong public hospital. PATIENTS. Patients with ruptured radiation-induced internal carotid artery pseudoaneurysms that were treated endovascularly from October 1999 to October 2011 at Queen Elizabeth Hospital were reviewed. Hospital records, imaging, and angiographic data were studied. RESULTS. During the study period, 15 such nasopharyngeal carcinoma patients were treated by endovascular means at Queen Elizabeth Hospital. Ten presented with epistaxis, three with otorrhagia (bleeding from the ear), and two with both. Therapeutic occlusion of the affected internal carotid artery was performed in four patients, and stenting of the artery (with or without coil obliteration of the pseudoaneurysm) was performed in 11. Immediate haemostasis was achieved in all cases. One (7%) of the 15 patients endured symptomatic recurrence of the pseudoaneurysm, and in another an asymptomatic residual pseudoaneurysm was noted in the follow-up angiogram. Three patients suffered clinically significant procedure-related complications, including cerebral infarction (n=2) and brain abscess (n=1). In the angiograms obtained after a mean post-treatment interval of 13 (range, 0.7-60) months, the stent patency rate was 67%. All three patients with occluded stents were asymptomatic. CONCLUSIONS. Ruptured internal carotid artery pseudoaneurysms following radiotherapy is a rare but life-threatening condition. Endovascular treatment by occlusion or reconstruction of the internal carotid artery with stents provides immediate haemostasis and obliteration of the pseudoaneurysms, with a low recurrence rate. Long-term follow-up is necessary to look out for delayed post-treatment complications.
    Hong Kong medical journal = Xianggang yi xue za zhi / Hong Kong Academy of Medicine 05/2013;
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    ABSTRACT: Vein of Galen aneurysmal malformation is a rare entity in the paediatric population. However, it is being recognised with increasing frequency due to better diagnostic techniques. Neonates usually present with congestive heart failure, while in older infants and children it tends to manifest with seizures, hydrocephalus, intracerebral or subarachnoid haemorrhages. We present a case of ruptured vein of Galen aneurysmal malformation in a 3-month-old baby boy treated by transarterial embolisation using Guglielmi detachable coils.
    Hong Kong medical journal = Xianggang yi xue za zhi / Hong Kong Academy of Medicine 10/2012; 18(5):435-8.
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    ABSTRACT: Intracranial aneurysm in twins is a rare clinical disease entity. Only 15 cases have been described in the literature. We report on a pair of identical twins with intracranial aneurysms. One presented with subarachnoid haemorrhage; digital subtraction angiography showed a left posterior communicating artery aneurysm, which was treated by coiling. The patient's twin sister was called for screening, whereupon digital subtraction angiography revealed a right ophthalmic internal carotid artery aneurysm that was treated conservatively.
    Hong Kong medical journal = Xianggang yi xue za zhi / Hong Kong Academy of Medicine 04/2011; 17(2):151-4.
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    ABSTRACT: It is hypothesized that a venographic-based operational classification of dural carotid-cavernous fistula (DCCF) will facilitate early selection of the optimal venous route and enhance the efficacy of transvenous catheterization and embolization of the cavernous sinus. This was a retrospective study on 97 patients who presented with symptomatic DCCF. Definition of classification type 1: both the anterior and posterior compartments of the cavernous sinus were opacified, type 2: only the anterior compartment was opacified, type 3: only the posterior compartment was opacified. Subtype a: the facial vein (FV) draining the superior ophthalmic vein (SOV) was opacified, subtype b: only the inferior petrosal sinus (IPS) was opacified, subtype c: neither the FV nor the IPS were opacified, subtype d: both the FV and the IPS were opacified. The SOV route was recommended for subtype 1a and type 2. The IPS route was recommended for subtype 1b, 1c, 1d, and type 3. Success rates of catheterization by the recommended routes and non-recommended routes were calculated. Number of DCCF lesions were 20 (1a), 28 (1b), 23 (1c), 26 (1d), 16 (2a), 10 (2c), 2 (3b). Of 145 attempted catheterization, 91 and 54 were performed with a recommended route and un-recommended route, respectively. Success rate for catheterization and embolization performed with the recommended route and un-recommended route was 71/91 (78%) and 20/54 (37%), respectively (Chi-Square test P = 0.0024). Venographic operational classification is useful for guiding the selection of optimal venous route which enhances the efficacy of transvenous embolization of the DCCF.
    Neuroradiology 12/2010; 53(12):993-9. · 2.70 Impact Factor
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    ABSTRACT: To review the pattern of ruptured intracranial aneurysms in terms of size, location, and the prevalence of multiple aneurysms in the Hong Kong Chinese population with subarachnoid haemorrhage. Retrospective study. Three public hospitals in Hong Kong. A total of 267 Chinese patients with subarachnoid haemorrhage from ruptured intracranial aneurysms between July 1998 and June 2002 were reviewed retrospectively. The patients had a mean age of 59 (range, 13-96) years, with a female-to-male ratio of 2:1. Concerning the age at presentation, males presented with ruptured intracranial aneurysms at a younger age (P=0.001) than females. Ruptured aneurysms were more commonly located in the anterior than posterior circulation (84% vs 16%). The posterior communicating artery (26%) and anterior communicating artery (22%) were the most common sites of rupture. As a whole, 64% of the aneurysms had a size of 5 mm or less. The anterior communicating artery had a higher proportion with a size of 5 mm or less compared to other locations (P<0.05). In this cohort, the prevalence of multiple aneurysms was 17%. There was no significant difference in the prevalence of multiple aneurysms between men and women (P=0.30). In patients with multiple aneurysms, the sizes of ruptured aneurysms were greater than those of the largest unruptured aneurysms (P<0.001). When compared with the group with single aneurysms, patients with multiple aneurysms had a smaller proportion of small aneurysms, sized 5 mm or less (P<0.05). The pattern of ruptured intracranial aneurysms in the Hong Kong Chinese population was different from western and Japanese populations. Although the distribution of locations for ruptured aneurysms was similar, Hong Kong Chinese had a larger proportion of small aneurysms sized 5 mm or less. The prevalence of multiple aneurysms in Hong Kong is comparable to that in the Japanese population, but lower than that in the western populations.
    Hong Kong medical journal = Xianggang yi xue za zhi / Hong Kong Academy of Medicine 09/2009; 15(4):262-6.
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    ABSTRACT: Dementia is a common medical problem that affects elderly patients. We report on a 77-year-old man with an intracranial dural arteriovenous fistula who presented with dementia that was initially thought to be irreversible and degenerative. Subsequent neuroendovascular intervention resulted in significant functional and cognitive improvement.
    Hong Kong medical journal = Xianggang yi xue za zhi / Hong Kong Academy of Medicine 03/2006; 12(1):74-6.
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    ABSTRACT: Patients with dural arteriovenous fistula (DAVF) are at higher risk of developing neurological deficits when there is retrograde leptomeningeal venous drainage. Our aim is to demonstrate the presence of dilated deep medullary veins in the brain on magnetic resonance imaging (MR) in this group of patients, and to assess their clinical significance. Nine patients with angiographically proven DAVF associated with leptomeningeal venous drainage who had MR before treatment were studied.MR was performed in at least two orthogonal planes before and after gadolinium administration. The dural fistula was located at the cavernous sinus in five patients, at the transverse-sigmoid sinus in three and at the tentorium in one. Dilated deep medullary veins were noted in six patients. Of these, four showed parenchymal abnormalities which included intracerebral haematoma, venous infarction, brain oedema and T2 hyperintensity in brainstem. Venous varix was present in one patient. No neurological complication or parenchymal change was observed in the three patients without dilated deep medullary veins. Therefore, in patients with intracranial DAVF associated with leptomeningeal venous recruitment, the MR finding of dilated deep medullary veins suggests a more severe degree of venous hypertension and congestion in the brain. This subgroup of patients has a much higher chance of neurological complications and warrants urgent intervention.
    Interventional Neuroradiology 09/2002; 8(3):265-72. · 0.77 Impact Factor
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    ABSTRACT: We investigate the dynamic stability of two interacting Bose-Einstein condensates moving through each other with a relative velocity vr. We show that there exists a critical velocity vr(c) such that for vr>vr(c) the condensate mixture becomes unstable. We construct an analytic expression of the critical relative velocity and determine the unstable collective modes. We also discuss how our results can be applied to matter-wave-mixing processes.
    Physical Review A 05/2001; 63(6). · 3.04 Impact Factor
  • T C Tan, C M Chan, H M Chiu
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    ABSTRACT: An anterior cerebral artery traumatic aneurysm in a 15-month-old infant is described. The diagnosis was confirmed by computed tomographic angiography. The patient recovered fully after successful clipping of the aneurysm. As the signs of traumatic intracranial aneurysm may be subtle especially in young children, a high degree of suspicion is essential in patients presenting with delayed neurological deterioration after head trauma.
    British Journal of Neurosurgery 05/2001; 15(2):137-9. · 0.86 Impact Factor
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    ABSTRACT: Haemorrhage from rupture of petrous ICA aneurysm can be life threatening and emergency treatment is required. We report 2 cases of radiation-induced petrous internal carotid artery (ICA) aneurysm presenting with acute haemorrhage (epistaxis and otorrhagia) after radiotherapy (RT) for nasopharyngeal carcinoma (NPC). Both patients had a history of RT treatment for NPC. The first patient, a 54-year-old man, presented with sudden severe epistaxis and haemorrhagic shock. The second patient, a 35-year-old man, presented with episodes of severe otorrhagia. The first patient was immediately resuscitated. Obliteration of the aneurysm was performed by endovascular occlusion of the ICA with Guglielmi detachable coils and fibered platinum coils. For the second patient, the aneurysm was treated by deploying a self-expandable stent across the aneurysm neck. In an emergency situation, ruptured petrous ICA aneurysm can be treated with endovascular occlusion of the ICA with microcoils if there is a good collateral blood flow. Alternatively, the aneurysm can be treated by deployment of a stent, which can induce stasis and eventual thrombosis of the aneurysm.
    Acta Neurochirurgica 02/2001; 143(4):351-5; discussion 355-6. · 1.55 Impact Factor
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    ABSTRACT: Hemorrhage in late cerebral radiation necrosis is a rare complication after radiotherapy for intracranial and extracranial neoplasms. We report 5 cases of acute hemorrhage in late radiation necrosis of the temporal lobe following radiation therapy for nasopharyngeal carcinoma. In a review of the literature, the authors identified a total of 27 such cases. The interval period between the onset of hemorrhage and cranial irradiation is long (mean = 7.8 years). The most prominent histological feature was the proliferation of large, dilated and thin-walled new blood vessels in a background of gliosis and fibrinoid necrosis of vessels. Rupture of these thin-walled new blood vessels is the proposed mechanism of hemorrhage in this condition.
    Journal of Neuro-Oncology 02/2001; 51(2):143-50. · 3.12 Impact Factor
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    ABSTRACT: Meningiomas are rare in childhood and they constitute 1.5% of intracranial meningiomas. We report a case of a left middle cranial fossa meningioma in a 11-year-old boy who presented with left-sided facial weakness and deafness. Neurological examination showed left lower motor neuron facial nerve palsy with sensori-neural deafness of his left ear.Computed tomography demonstrated a contrast enhancing extra-axial tumour in the left middle cranial fossa with calcification. Magnetic resonance imaging confirmed the presence of an extra-axial tumour measuring 3 × 3.5 × 2.7 cm. The mass was isointense to gray matter on T1-weighted images, with a markedly hypointense rim on T2-weighted images. The lesion exhibited homogeneous enhancement with gadolinium. It eroded the petrous base, extending into the left internal auditory meatus and cerebello-pontine cistern. The preoperative diagnosis was trigeminal schwannoma.Intraoperatively, a firm tumour was seen arising from the middle cranial fossa attached to the petrous temporal bone. Near-total excision of tumour was achieved. The histological diagnosis was xanthomatous meningioma. The patient recovered uneventfully without additional neurological deficit. He underwent linac radiosurgery for the 1 cm tumour remnants in the internal acoustic meatus and the left cerebellopontine angle. Follow-up MRI scans 14 months after radiosurgery showed shrinkage of the remaining tumour. At follow up 20 months after operation the child was well and had resumed his education.Conclusion: While surgery remains the main therapeutic modality, complete excision is not always possible in skull base meningiomas as it carries significant postoperative morbidity. Radiosurgery is a valuable complementary measure for local control in case of residual or recurrent tumour.
    Annals of the College of Surgeons Hong Kong 01/2001; 5(1).
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    ABSTRACT: A Reply to the Comment by Mourad Haddad and Vincent Hakim.
    Physical Review Letters 01/2001; 87. · 7.73 Impact Factor
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    CK Law, CM Chan, PT Leung, M Chu
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    ABSTRACT: We present an exact analytic solution of a nonlinear Schrodinger field interacting with a moving potential (obstacle) at supersonic speed. We discover conditions under which the field can form a stable shape-invariant structure localized around the obstacle-a dressing effect that protects the field against excitations by the obstacle. Such an effect demonstrates the existence of frictionless motion beyond the conventionally defined critical velocity.
    Physical Review Letters 09/2000; 85(8):1598-601. · 7.73 Impact Factor
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    ABSTRACT: A four-layer feed-forward back-propagation artificial neural network (ANN) is applied to weather radar echo maps of reflectivity data for the prediction of heavy rainfall events in the short-range of 1 to 2 hours. Inputs for the ANN are the cross correlations of statistical measures of a sequence of radar images. The ANN is trained to capture increasingly organized echo patterns that often are preludes to localized heavy rain. Results show that the ANN is able to achieve a success rate of 89% against a false alarm rate of 33%. In parallel, a separate module utilizing Hough transform is developed to depict the lining up of echoes on the reflectivity maps. The module provides an objective analysis tool for forecasters to test the hypothesis that crossing or merging of echo lines, the so-called “X” patterns, would lead to enhanced convection at preferred locations. Working in tandem, the ANN helps to isolate specific sectors on the radar maps where organization is taking place so that the Hough transform module (HTM) can be meaningfully applied in the appropriate target areas. In turn, parameters derived from the HTM, along with the standard statistical measures, can be fed back into the ANN for further training and system enhancement in the identification of “X” patterns
    Pattern Recognition, 2000. Proceedings. 15th International Conference on; 02/2000
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    ABSTRACT: Radiation necrosis is a known complication following radiation therapy for extracranial as well as intracranial tumours. However, brain abscess formation in radiation necrosis has not been reported in the literature. We report the clinical data of 6 patients suffering from this condition. Twenty-eight patients with radiation necrosis of the temporal lobe following radiotherapy for nasopharyngeal carcinoma were treated surgically at the Department of Neurosurgery, Queen Elizabeth Hospital, Hong Kong between January 1992 and July 1999. Of these, 6 cases were complicated by brain abscess formation. The clinical data of these 6 patients are retrospectively reviewed. The patients were 5 males and 1 female, ranging in age from 41 to 67 years. Three patients had previous treatment with steroids for the symptomatic radiation necrosis. A history of nasal infection or otitis media was recognised in all 6 patients. All patients were treated surgically by temporal lobectomy and excision of the necrotic tissue together with the abscess cavity. Intra-operatively, a bony defect was observed between the middle cranial fossa and the sphenoid sinus in 3 patients and the bony defect was repaired with a temporalis muscle flap. The species of organisms could only be identified in 3 patients. In 3 patients, the pus smear was positive but the culture was negative. Subsequently, 4 patients recovered and 2 patients died. Cerebral radiation necrosis is a predisposing cause of brain abscess formation. Surgical excision is recommended as the treatment of choice in this group of patients.
    Acta Neurochirurgica 02/2000; 142(4):435-40; discussion 440-1. · 1.55 Impact Factor
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    ABSTRACT: There are two important pathological features associated with carotid-cavernous fistula (CCF): the retrograde cortical venous drainage that can cause intracranial haemorrhage and non haemorrhagic neurological deficit and the retrograde ophthalmic venous drainage that causes orbital venous congestion and visual impairment. We propose a sequential embolisation strategy by the selective occlusion of these two pathological features as the initial steps followed by occlusion of the rest of the cavernous sinus. Eight patients with spontaneous CCF were treated by transvenous embolisation using our embolisation strategy. The clinical features, angiographic findings, embolisation procedures, and clinical and angiographic outcomes were analyzed. The follow-up period ranged from one to 21 months. Clinical cure was achieved in six patients at one to two month follow-ups. One patient with bilateral CCFs had clinical cure of the right eye and clinical improvement of the left eye at three-month follow-up. Another patient had clinical cure at one-month follow-up except residual VI nerve palsy. Two patients had complete angiographic obliteration of the fistula immediately after the embolisation procedure. Another three patients underwent follow-up angiography at one to 16 months and all showed angiographic cure. There were no immediate or late complications. Our embolisation strategy offers a safe and effective option in the embolisation of spontaneous CCF as demonstrated by the clinical results of our eight patients.
    Interventional Neuroradiology 09/1999; 5(3):225-34. · 0.77 Impact Factor
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    ABSTRACT: We give a preliminary report of the ophthalmologic outcome of four patients with transvenous embolization studied for their spontaneous carotid-cavernous fistulas. One of them is a direct type while three of them are indirect dural shunts. In indirect dural shunts, traditional transarterial embolization rarely achieves a complete clinical cure in a short period of time. All cases had an ophthalmologic disturbance justified for endovascular intervention. We performed catheterization, and subsequently embolization with Guglielmi Detachable coils, to the cavernous sinus via the femoral vein and inferior petrosal sinus/superior ophthalmic vein. All four patients achieved clinical and angiographic improvement with a follow-up period range from two to sixteen months except for one patient who had residual bilateral sixth nerve palsy. The transvenous approach offers an effective and safe alternative for the management of spontaneous carotid-cavernous fistula.
    International Ophthalmology 02/1999; 23(1):43-7.
  • K M Cheng, M W Ma, C M Chan, C L Leung
    Acta Neurochirurgica 02/1997; 139(12):1189-90. · 1.55 Impact Factor