Dear Editor,

Decompressive craniectomy is a common procedure performed for raised intracranial hypertension with obligatory subsequent bone flap replacement or cranioplasty at varying intervals, for various side effects of the lack of bone flap, well described in the literature. However, the complications during and following the replacement of bone flap did not strike the limelight, which may require another surgical intervention.[ 1 – 3 ] Sinking of entire bone flap following the cranioplasty procedure is much more than cosmesis for the antecedent neurological deficits it produces; hence righteously qualifies to be termed as “sunken bone flap syndrome”.

A 35-year-old male who underwent right fronto- temporo- parietal decompressive craniectomy for right temperoparietal contusion sustained following road traffic accident 7 years ago. The bone flap was replaced after 2 months and was fixed with two clamps. Patient was asymptomatic for 6 years when he noticed gradually progressive weakness involving his left upper and lower limbs, associated with sinking of the bone into the parenchyma and worsening of his hemiparesis to hemiplegia. There was no history of any trauma prior to the onset of symptoms. Computed tomography (CT) brain revealed sunken free bone flap, breaking the clutches of the bone clamps used to fix the bone flap, causing midline shift and mass effect [ Figure 1 ]. Patient underwent re-exploration. Intraoperatively, two undisplaced metallic clamps, used during previous surgery, were noticed to be fixed to the skull, which had lost the grip on the free flap. The metallic clips were removed and adhesiolysis between the dura and the bone flap was done and the bone flap fixed meticulously.

Figure 1

Computed tomography scan of brain demonstrating the sunken bone flap into the depths, compressing the brain parenchyma and causing midline shift and mass effect

The pathophysiological mechanism ascribed to the neurological deterioration include (a) the alteration of vascular flow both in sunken skin and bone flaps; with improvement following proper cranioplasty reverting the normal blood flow and (b) secondary diaschisis.

Free bone flap, devoid of its periosteum, and subjected to resorptive mechanisms both during the storage in the abdominal parieties and on replacement, requires a firm fixation. Patients with ventriculo-peritoneal shunt are at higher risk of complications following cranioplasty when compared with non shunted patients and in particular this complication can be attributed to over function of shunts.[ 4 ] The unequal pressure dynamics do not end with the replacement of bone flap, but requires probably a larger perspective of assembly of the free flap with the rest of the cranium, resetting the equilibrium once for all. Last but not the least financial constraints, especially in developing countries, limits the usage of adequate implants, and a firm fixation.

A concrete fixation of the bone flap following a decompressive craniotomy with judicious and adequate clamps is essential.

References

1. Anei R, Uemori G, Orimoto R, Saito M, Hirosima S, Mitsui N. A case of brain herniation due to delayed bone flap sinking. No Shinkei Geka. 2010. 38: 923-6

2. Del Mar Carmona Abellán M, Murie Fernández M, Esteve Belloch P. Cranioplasty sinking should affect normal brain function mimicking other neurologic illness. AJNR Am J Neuroradiol. 2012. 33: E65-

3. Gooch MR, Gin GE, Kenning TJ, German JW. Complications of cranioplasty following decompressive craniectomy: Analysis of 62 cases. Neurosurg Focus. 2009. 26: E9-

4. Schuss P, Vatter H, Marquardt G, Imöhl L, Ulrich CT, Seifert V. Cranioplasty after decompressive craniectomy: The effect of timing on postoperative complications. J Neurotrauma. 2012. 29: 1090-5