=====Interhemispheric hygroma (IHH)=====

//Juan Sales-Llopis//


//Department of Neurosurgery, General University Hospital Alicante, Spain//

[[Craniectomy]] close to the midline can predispose patients to the development of [[hydrocephalus]]. Interhemispheric [[subdural hygroma]] could be generated with the same mechanism, and these three events could be correlated on a timeline

De Bonis et al. ((De Bonis P, Sturiale CL, Anile C, Gaudino S, Mangiola A, Martucci M, Colosimo C, Rigante L, Pompucci A. Decompressive craniectomy, interhemispheric hygroma and hydrocephalus: a timeline of events? Clin Neurol Neurosurg. 2013 Aug;115(8):1308-12. doi: 10.1016/j.clineuro.2012.12.011. Epub 2013 Jan 3. PubMed 
PMID: 23290122.))
hypothesized that a medial craniotomy may have a potentially pathogenetic role in the development of [[posttraumatic hydrocephalus]] (venous blood flow theory). Nonetheless, this [[hypothesis]] does not explain why the resolution of hydrocephalus after bone flap replacement was observed only in some patients. Probably, there are several factors related to the pathogenesis of IHH and posttraumatic hydrocephalus, and they work together in the development of ventricular enlargement. Further studies are necessary to understand these questions, the real relationship between decompressive craniectomy and posttraumatic hydrocephalus, and how these factors modify prognosis
((Kaen A, Jimenez-Roldan L, Alday R, Gomez PA, Lagares A, Alén JF, et al: Interhemispheric hygroma after decompressive craniectomy: does it predict posttraumatic hydrocephalus? Clinical article. J Neurosurg 113:1287–1293, 2010)).


Aarabi et al.
((Aarabi B, Hesdorffer DC, Simard JM, Ahn ES, Aresco C, Eisenberg HM, et al: Comparative study of decompressive
craniectomy after mass lesion evacuation in severe head injury. Neurosurgery 64:927–940, 2009))
reported that, in 54 patients with severe head injuries who underwent [[decompressive craniectomy]] (DC) with evacuation of mass lesions, 15 patients developed [[subdural hygroma]]s, that 10 (67%) of these patients exhibited IHHs, and that hydrocephalus was observed in 4 of the 15 patients with subdural hygromas. These data are in accord with the results of Kaen et al. 
((Kaen A, Jimenez-Roldan L, Alday R, Gomez PA, Lagares A, Alén JF, et al: Interhemispheric hygroma after decompressive craniectomy: does it predict posttraumatic hydrocephalus? Clinical article. J Neurosurg 113:1287–1293, 2010)).

In contrast, Aarabi et al.
((Aarabi B, Hesdorffer DC, Ahn ES, Aresco C, Scalea TM, Eisenberg HM: Outcome following decompressive craniectomy for malignant swelling due to severe head injury. J Neurosurg 104:469–479, 2006))
previously reported that, of 50 patients with severe head injuries who underwent DC without removal of clots or contusion for diffuse brain swelling, 25 patients developed subdural hygromas, which were rarely interhemispheric. 

Thus, the studies by Kaen et al. and Aarabi et al. suggest that the high incidence of IHH might be the result of DC with evacuation of mass lesions. 

Therefore, Takeuchi et al. hypothesize that the volume of the evacuated mass may be correlated with the occurrence of IHHs. As such, DC with evacuation of large mass lesions may generate a greater suction effect
and the interhemispheric space is more likely to expand.
If this hypothesis is correct, careful attention should be paid to the occurrence of IHHs, especially when DC with evacuation of large mass lesions is performed. Further investigation into the correlation of the volume of evacuated mass lesions with occurrence of IHHs may provide additional insight into the mechanism of IHHs after DC
((Takeuchi S, Nagatani K, Otani N, Nawashiro H. Interhemispheric hygroma. J Neurosurg. 2011 Jul;115(1):194-5; author reply 195. doi: 10.3171/2011.2.JNS11122. Epub 2011 May 6. PubMed PMID: 21548753.)).