Decompressive craniectomy is performed to reduce risk of brain herniation in the setting of severe or medically refractory intracranial hypertension. Sinking skin flap syndrome (SSFS), also known as “syndrome of the trephined” (ST) is a rare complication of decompressive craniectomy, with only 83 cases reported as of 2013, although it is probably underdiagnosed.1,2 Along with neurological deterioration, the syndrome is characterized by a sunken skin flap over the defect that can progress to a “paradoxical brain herniation,” leading to rapid further decline without prompt intervention.3 The timing of symptom onset postcraniectomy varies; however, it usually occurs after several weeks or months.1,2 With written informed consent from the patient, we report a case of relatively early-onset SSFS, with rapid symptom improvement after supine positioning, and resolution after cranioplasty.
A 58-year-old man with pertinent history of hypertension and tobacco use presented after sudden collapse with chest pain and “stroke-like symptoms.” Computerized tomography (CT) angiogram revealed Stanford type A aortic dissection with complete occlusion of the right common carotid and internal carotid arteries. He subsequently underwent emergent repair with aortic valve replacement, aortic root, ascending aorta, and hemiarch replacement. Postoperative neurological assessment revealed dense left hemiplegia. On postoperative day 1, brain CT revealed large right middle cerebral artery territory acute nonhemorrhagic infarct with localized mass effect (Figure 1A). Nonetheless, his hemodynamic and neurological status improved sufficiently to permit extubation. However, over the next 48 hours, his neurological status progressively declined.
On postoperative day 3, repeat brain CT showed infarct evolution with significant mass effect including uncal and subfalcine herniation (Figure 1B). Management included osmotic therapy with mannitol and hypertonic saline, and urgent decompressive right hemicraniectomy (Figure 1C). Immediately postcraniectomy, his Glasgow Coma Scale (GCS) was 10T. After extubation, serial neurological examinations revealed the patient to be alert, oriented, and appropriately responsive to commands, with residual left hemiparesis: He could withdraw his left lower extremity to pain but could not move his left upper extremity. With supportive management including physical therapy, he progressed to sitting in a chair for longer durations daily.
After craniectomy, CT images were obtained with any significant changes in mental status (Figure 2). By postcraniectomy day (PCD) 14, increasing somnolence and lethargy were noted with GCS of 9. Brain CT showed stable mass effect, 7 mm right-to-left midline shift, and mild hemorrhagic conversion. There was no evidence of infection or metabolic derangements, and continuous electroencephalographic (EEG) monitoring was negative for seizures. The next 2 weeks were notable for difficulty following simple commands, concave depression of the right hemicranium, and fluctuating sensorium. His GCS ranged from 8 to 13, with a transient nadir of 3 on PCD 20. Brain CT then showed 9 mm right-to-left midline shift and subfalcine herniation. A CT angiogram to assess for basilar occlusion was negative. This pattern of waxing and waning neurological status continued with progressively longer intervals of impaired sensorium. On PCD 27, brain CT revealed stable 9 mm right-to-left midline shift with subfalcine herniation, right lateral ventricular effacement, and left lateral ventricular trapping.
The collective findings of sunken skin flap, concave cerebral depression and midline shift in serial images, and lack of metabolic abnormality, seizures, or delirium led to a diagnosis of SSFS. Accordingly, the patient was repositioned from 45° recumbent to 15°. Within 30 minutes, his neurological status began improving and he was then laid completely supine. Over the next hour, he was completely awake and back to his best postoperative baseline. Subsequently, he was mostly maintained in supine position until a right cranioplasty with replacement of the bone flap was performed on PCD 35. Postcranioplasty head CT showed improvement of previous findings, including reversal of the midline shift. Through the remaining hospital stay, he remained stable and cognitively improved regardless of position, with moderate residual left upper extremity weakness.
ST was first described as an indication for cranioplasty by Grant and Norcross4 in 1939. That initial description included severe headache, dizziness, fatigue, surgical site discomfort, apprehension and insecurity, mental depression, and intolerance of vibration.4 Later, “syndrome of the sinking skin flap” was described by Yamaura and Makino5 and was considered a separate entity from ST. Both syndromes occurred in postcraniectomy patients: ST was described using subjective measures, while SSFS was described as “concave deformity” or “sinking” of the skin flap, occurring weeks to months after craniectomy, along with secondary neurological and EEG deterioration, which could be reversed with bone replacement.5
Subsequent descriptions in case reports varied with some overlap. This discrepancy led to efforts to unify and identify the “classic” clinical presentation.1 To this end, Ashayeri et al6 conducted a systematic review of patients who developed neurological symptoms after large-sized craniectomy and showed clinical improvement after cranioplasty. The results demonstrated that SSFS can occur in all ages, with male predominance (60%). Average onset of symptoms after craniectomy was about 5 months with wide variability. Improvement after cranioplasty was 4 days, often occurring within 24 hours. Motor deficits (57%) and cognitive decline (41%) were the most commonly reported symptoms, while headache occurred less frequently (19%). Although accounts exist of cognitive decline without a sinking skin flap, the review found that 93% of authors reported a visibly sunken flap. In 5 studies that evaluated EEG activity before and after cranioplasty, all noted improvement in seizure activity postcranioplasty.6
Similar characteristics were described in a review by Annan et al1 that compared the original description by Grant and Norcross4 to symptoms reported in other publications. Vague discomfort at the site of defect, apprehension and insecurity, and intolerance to vibration were not observed. Dizziness and fatigability were rarely described. Rather, principal symptoms included sensorimotor impairment, cognitive disturbances, and headache (Table). Symptoms almost always corresponded with daytime and upright position.1,2,6 In general, although SSFS seems to be rare, this may partly be due to underreporting. In 1 review of 64 craniectomy patients, the incidence was estimated to be 7.8%.2
The postulated pathophysiology of SSFS begins with brain exposure to atmospheric pressure (760 mm Hg; 14.7 lb/in2, 1 atm sea-level) via the cranial defect, resulting in progressive sinking of the skin flap, with external compression of the underlying brain. This so-called external tamponade of the brain is thought to impair cerebrospinal fluid (CSF) and cerebral blood flow (CBF), and alter glucose metabolism leading to cortical dysfunction.6 Improvement in CBF after cranioplasty has been demonstrated via multiple imaging modalities, in bilateral hemispheres.1,6 Similarly, improved CSF hydrodynamics after cranioplasty has also been shown by dynamic magnetic resonance imaging.7 Last, improved CBF and metabolism after cranioplasty have been demonstrated, using enhanced magnetic resonance spectroscopy to determine the ratio of phosphocreatine to inorganic phosphate as an index of cerebral energy depletion.8 Paradoxical herniation can occur due to combined extracranial gravitational and atmospheric forces acting on intracranial contents. This results in midline deviation, mass effect, and subfalcine, uncal, or transtentorial herniation of intracranial contents despite craniectomy defect.3,9,10 Increased susceptibility is seen with lowering of intracranial pressure due to altered CSF pressure with external ventriculostomy, ventriculoperitoneal shunting, or lumbar puncture.3,9,11
Definitive treatment is cranioplasty in the absence of ongoing edema, mass effect, or hydrocephalus.3 Time to cranioplasty is often delayed by various aspects of patient care, with the most-cited cause being infection or leukocytosis.6 During the interim, supine or Trendelenburg positioning, hydration, and clamping CSF drainage, or even intrathecal infusion of fluids, may alleviate symptoms. This is essentially the opposite of traditional herniation treatment aims to reduce intracranial pressure with mannitol, CSF drainage, and hyperventilation as described by the Monro-Kellie doctrine.9,10 Hemorrhagic infarction has rarely (5 cases) been reported after cranioplasty for SSFS treatment.12
The wide variability in onset timing and clinical syndrome description may result in underrecognition and signifies the need for ongoing neurological evaluation for several months after craniectomy. While timing from craniectomy to symptom development is variable, early development of SSFS is rarely described. Four cases have occurred within a week of surgery in the presence of additional contributing factors such as lumbar CSF leak.1 Schiffer et al13 described several cases highlighting the variable time course, of which 2 cases occurred at 48 hours and 7 days postoperatively; however, both of these cases were in the setting of CSF drainage via ventriculoperitoneal shunt and repeated lumbar puncture, which may have accelerated the pathophysiological development.6 Joseph and Reilly14 reported a case that presented 9 days postcraniotomy in the absence of contributing factors.
We have reported early development of SSFS with paradoxical herniation 2 weeks after surgery, coinciding with intervals of upright positioning, in the absence of iatrogenic or incidental CSF drainage. Serial CT images demonstrated progressive midline shift, mass effect, and subfalcine herniation consistent with paradoxical herniation. After diagnosis and supine positioning, improvement occurred within 1 hour. Resolution of symptoms to baseline occurred within a few days after cranioplasty. Due to the rarity and variability in onset and severity, this potentially devastating condition may present in any intensive care setting, as in our case. Prompt recognition and treatment by critical care providers of any specialty is of utmost importance to avoid neurological deterioration and to promote recovery.
Name: Nicholas Fawley, DO.
Contribution: This author helped review the literature, prepare the draft, and revise the manuscript.
Name: Chiedozie Udeh, MBBS, FCCP.
Contribution: This author helped review the literature, prepare the draft, and revise the manuscript.
This manuscript was handled by: Mark C. Phillips, MD.
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