Introduction 

   Remote cerebellar hemorrhage (RCH) after supratentorial craniotomy is an infrequent and poorly understood complication. Although RCH have been described several times in some literatures,^{2)3)8)10)11)12)} its etiology and mechanism have been unclear. We will present 2 cases of RCH after aneurysm surgery and discuss the common findings in both cases. And we reviewed the previous literatures. 

Case reports 

Case 1 
   The patient was a 57-years-old man who was admitted for unruptured aneurysm surgery of an incidental aneurysm of the anterior communicating artery (Acom). He had no significant medical history, except for photoallergic dermatitis and laboratory study could not show any coagulopathy. Preoperative digital subtraction angiography (DSA) showed the unruptured Acom aneurysm without any other remarkable findings and both transverse sinuses were well shown in the venous phase of right vertebral angiogram (Fig. 1A, B). Aneurysm clipping was performed by usual pterional approach. During operation, he was hemodynamically stable. However, in the recovery room, systolic blood pressure (SBP) was up to 170mmHg. Postoperative CT brain images showed the remote cerebellar hemorrhage (Fig. 2A). However, he did not have any neurological deterioration except headache. He did not have any other surgical procedure and was discharged without neurologic deficit. One month after surgery, follow up CT showed the resolution of hemorrhage (Fig. 2B). 

Case 2 
   The patient was a 59-years-old woman who was admitted for incidental Acom aneurysm surgery. She had a history of hypertension and diabetes mellitus. Preoperative DSA showed the unruptured Acom aneurysm with poorly visualized left transverse sinus (Fig. 3A, B). Aneurysm clipping was performed by usual pterional approach. During operation, she was hemodynamically stable and SBP never exceeded 140mmHg. However, during the waking-up from anesthesia, SBP elevated up to 165mmHg suddenly. Although postoperative brain CT showed the remote cerebellar hemorrhage (Fig. 4A), the patient had no neurologic deterioration. On postoperative day 2, the patient s mentality became stuporous. Follow-up CT showed increasing cerebellar hematoma with acute obstructive hydrocephalus (Fig. 4B, C). Emergent decompressive suboccipital craniectomy and hematoma removal was performed. At postoperative month 1, she was fully recovered except mild gait disturbance and discharged. 
   The characteristics of the 2 patients are summarized in Table 1. 

Discussion 

   RCH after supratentorial craniotomy is uncommon and poorly understood complication. Sometimes it can cause fatal neurologic deterioration.¹⁾⁵⁾ Some cases have been published in the literature. Konig et al showed an incidence of RCH after superatentorial craniotomy to be approximately 0.3%.⁷⁾ Cloft reported a higher incidence of about 3.5% after aneurysm surgery.³⁾ An incidence of 4.9 % after temporal lobectomy was reported by Toczek et al.¹⁰⁾ However, its etiology and pathophysiology is not clear. 
   Many theories have been proposed to explain the pathophysiology of RCH. We reviewed literatures and summarized them as below: 
   First, cerebrospinal fluid (CSF) overdrainage induces downward displacement of the cerebellum, and mechanical disturbance in the venous system, which leads to stretching or tearing of bridging vermian or posterior mesencephalic veins and tirbutaries.^5)11)13) As a result, venous blockade and hypertension are evoked and lead to cerebellar hemorrhage. Also, Poppen and colleagues reported that RCH from following supratentorial surgery could result in a blockade of venous drainage due to brain swelling and increased supratentorial pressure.⁹⁾ Second, another group of authors proposes that acute loss of CSF and craniotomy induce negative supratentorial and intracranial pressure, which can result in a reciprocal increase in the transmural pressure in veins and venules, traumatize the cerebellar capillaries, and cause intracerebellar hemorrhage.⁶⁾⁷⁾ Third, Farag E. and colleagues suggest that head rotation and neck flexion can induce positional jugular vein compression which leads to venous hypertension and hemorrhage.⁴⁾ Although most authors agree that the main pathophysiology of RCH is the venous infarction, most literatures did not explain about venous drainage pattern of preoperative DSA. Tucker and colleagues reported that the angiographic finding did not show any other vascular abnormalities.¹¹⁾ 
   In our second case, the ipsilateral transverse sinus was poorly visualized on preoperative DSA. However, angiographic abnormalities were not shown in the first case. Although concomitant findings were not shown in DSA, It was possible for poorly drained transverse sinus in preopretive DSA to be a contributor of RCH and more severe cerebellar edema. Actually, in the second case, the patient had more extensive hemorrhage, aggressive course and neurologic deterioration. Less functioning transverse sinus amplified stretching and tearing of bridging vein which lead to extensive RCH. Forth, Friedmann and colleagues found that elevated intraoperative systolic blood pressure was independent risk factor associated with RCH.⁵⁾ In our cases, intraoperative blood pressure were stable. However, postoperative SBP elevated suddenly and could not be well controlled. 
   It is thought for the pathophysiology of RCH to be complex including CSF overdrainage, venous flow disturbance, intracranial hypotension, arterial hypertension and head position.(Fig. 5) We can have one question; How can we prevent RCH? First, preoperative DSA should be reviewed by experienced neurosurgeon to identify venous drainage pattern. Second, extreme head rotation and flexion should be avoided for release jugular vein. Finally, after supratentorial craniotomy, expert of neurosurgical anesthesia should emergence the patient carefully to control blood pressure. 

Conclusion 

   In spite of rarity, RCH can cause fatal outcome. And it can be related with several factors. Neurosurgeons should be aware of its possibility and if preoperative DSA show less drained venous system, more careful attention can prevent this complication. 

REFERENCES

1. Brockmann MA, Groden C. Remote cerebellar hemorrhage: a review. Cerebellum 5:64-8, 2006 

2. Calisaneller T, Yilmaz C, Ozger O, Caner H, Altinor N. Remote cerebellar haemorrhage after spinal surgery. Can J Neurol Sci 34:483-4, 2007 

3. Cloft HJ, Matsumoto JA, Lanzino G, Cail WS. Posterior fossa hemorrhage after supratentorial surgery. AJNR Am J Neuroradiol 18:1573-80, 1997 

4. Farag E, Abdou A, Riad I, Borsellino SR, Schubert A. Cerebellar hemorrhage caused by cerebrospinal fluid leak after spine surgery. Anesth Analg 100:545-6, 2005 

5. Friedman JA, Piepgras DG, Duke DA, McClelland RL, Bechtle PS, Maher CO, et al. Remote cerebellar hemorrhage after supratentorial surgery. Neurosurgery 49:1327-40, 2001 

6. Honegger J, Zentner J, Spreer J, Carmona H, Schulze-Bonhage A. Cerebellar hemorrhage arising postoperatively as a complication of supratentorial surgery: a retrospective study. J Neurosurg 96:248-54, 2002 

7. Konig A, Laas R, Herrmann HD. Cerebellar haemorrhage as a complication after supratentorial craniotomy. Acta Neurochir 88:104-8, 1987 

8. Konya D, Ozgen S, Pamir MN. Cerebellar hemorrhage after spinal surgery: case report and review of the literature. Eur Spine J 15:95-9, 2006 

9. Poppen JL, Kendrick JF Jr, Hicks SF. Brain stem hemorrhages secondary to supratentorial space-taking lesions. J Neuropathol Exp Neurol 11:267-79, 1952 

10. Toczek MT, Morrell MJ, Silverberg GA, Lowe GM. Cerebellar hemorrhage complicating temporal lobectomy: report of four cases. J Neurosurg 85:718-22, 1996 

11. Tucker A, Miyake H, Tsuji M, Ukita T, Nishihara K. Remote cerebellar hemorrhage after supratentorial unruptured aneurysmal surgery: report of three cases. Neurol Res 29:493-9, 2007 

12. Srikijvilaikul T, Deesudchit T. Cerebellar hemorrhage after supratentorial surgery for treatment of epilepsy: report of two cases. J Med Assoc Thai 90:1221-4, 2007 

13. Yoshida S, Yonekawa Y, Yamashita K, Ihara I, Morooka Y. Cerebellar hemorrhage after supratentorial craniotomy: report of three cases. Neurol Med Chir 30:738-43, 1990