Three-Dimensional Computed Tomography Reconstruction Unmasks Shunt Disconnection in a Child

An 18-month-old patient with complex postinfectious hydrocephalus presented with suspected shunt malfunction. The infant was vomiting intermittently for over a month, but her clinical appearance was reassuring. She was alert with no focal neurological deficits. The fontanelle was closed and papilledema was absent. Cranial imaging demonstrated ventriculomegaly (Figure 1A) but prior cross-sectional imaging was unavailable for comparative review. The shunt X-rays and axial computerized tomography (CT) did not reveal an obvious shunt disconnection (Figure 1B). We were unable to aspirate cerebrospinal fluid from the shunt, but her symptoms resolved spontaneously soon after admission. A diagnosis of arrested hydrocephalus and a viral illness was suspected. She re-presented with emesis 7 days later. Again, her clinical status was reassuring with no impairment of consciousness or signs of raised intracranial pressure. A repeat CT scan showed stable ventriculomegaly and no obvious shunt disconnection was apparent on repeat X-rays.

Figure 1: (A) Axial T2 MRI showing ventriculomegaly and encysted ventricles. (B) Skull X-ray showed no obvious disconnection.

We elected to explore the shunt in the operating room the day after admission. Intraoperatively, an unexpected disconnection was identified between the proximal ventricular catheter and shunt valve. Correction of this problem quickly led to resolution of the patient’s symptoms. We re-reviewed the preoperative imaging at initial presentation and during her repeat admission but could not visualize the disconnection (Figure 1A and B). However, we retrospectively obtained 3D reconstructions of the CT scans, which clearly demonstrated the disconnection (Figure 2). This case emphasizes the value of obtaining 3D-CT reconstructions in the context of suspected shunt malfunction, especially in the pediatric patient who may not exhibit overt clinical or radiological signs. Earlier identification of the disconnection via 3D-CT imaging may have enhanced decision making, avoided a discharge and readmission, and facilitated prompter treatment.

Figure 2: 3D reconstruction of CT head scan prior to shunt exploration showed clear disconnection of the proximal catheter from the shunt valve.

Shunt disconnection is the cause of malfunction in approximately 10% of cases.¹ Diagnosing shunt disconnection with shunt series X-rays may prove difficult as the disconnection may be subtle, as in our case, and the shunt may still be partially functional which can manifest as inconsistent and intermittent symptoms.^2,3 The negative predictive value of shunt series X-rays is only 22%.⁴ 3D visualization of the shunt by reconstruction of a multidetector CT scan provides much better clarity of shunt components.³ These 3D reformats can be easily generated from the original CT dataset from a multidetector CT available in most imaging departments today and do not require any increased radiation dose.

In summary, 3D-CT reconstructions retrospectively proved to be diagnostic of a subtle shunt disconnection in a child with ambiguous clinical and radiological signs of shunt malfunction. In our institution, patients with suspected shunt malfunction who have CT brain imaging on admission are now receiving routine radiological evaluation with 3D-CT reconstructions to facilitate the detection of obscure shunt fractures and disconnections.