Introduction

Dandy-Walker malformation (DWM) is a rare congenital malformation involving the posterior fossa, affecting 1/25000–30,000 live births [3, 4, 20]. Diagnosis is based on classical radiological features, which include (1) upward and backward rotation of hypoplastic cerebellar vermis and (2) posterior fossa cyst [4]. At the initial diagnosis, 80% of the patients present hydrocephalus, which represents the most common complication of this malformation [20]. The co-existence of DWM and syringomyelia is rare, and only 23 cases have been reported so far [1, 5,6,7,8,9,10,11, 13,14,15,16,17,18,19, 21,22,23]. According to the available literature, pathogenic hypotheses, best surgical approach, and outcome remain poorly defined.

We report on a girl with DWM and concomitant holocord syringomyelia that presented with severe cervicalgia. The clinical course, surgical approach, and outcome are described, and possible mechanisms of syrinx formation are discussed.

Case presentation

A 2-month-old girl underwent head CT for progressive macrocrania without other symptoms. Neuroimaging diagnosed a DWM with mild supratentorial ventricular dilation that was clinically and radiologically monitored. At the age of 2, a VPS was placed for symptomatic hydrocephalus with good postoperative outcome. In 2013, an MRI was performed to investigate a growth deficiency associated to low levels of serum somatomedine C: neuroimaging showed a holocord syrinx associated with herniation of the posterior fossa cyst through the foramen magnum (Fig. 1a, b).

Fig. 1
figure 1

MRI exams in our DWM girl. a Sagittal T2-weighted image of the brain showing the upward and backward rotation of the hypoplastic cerebellar vermis; a large cyst occupies the posterior cranial fossa and its wall is protruding in the foramen magnum (black arrowhead). b–d Midsagittal T2-weighted images of the cervical spine showing the syrinx at diagnosis (b; *), its cervical progression after ventriculo-peritoneal shunt revision (c; white arrows) and its complete regression after cyst-peritoneal shunting (d). e, f Midsagittal T1-weighted images of the posterior cranial fossa disclosing the infratentorial cyst after ventriculo-peritoneal shunt revision (e) and its detension after cyst-peritoneal shunting (f)

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Surgery

Despite the absence of supratentorial hydrocephalus progression, a shunt malfunction was considered and the VPS was revised. During surgery, a distal malfunction of the system was found and both distal catheter and the programmable valve were changed. After few weeks, she started to complain about a neck pain, which progressively impaired daily activities. The follow-up MRI showed a reduction in size of the medio-dorsal part of the syrinx but an increase of the cranial portion of its cervical part (Fig. 1c), prompting for a CPS connected to VPS beyond the programmable valve with a Y-connector, deferring a more invasive surgery such as a suboccipital decompression with C1 laminectomy and cyst decompression in the case of failure.

Follow-up

Postoperatively, the girl made a good recovery and there were no complications related to the surgery. The neck pain progressively disappeared. The follow-up MRI showed the reduction in size of the syrinx that completely regressed 1 year after surgery (Fig. 1d). After a 4-year follow-up, she is neurologically intact without recurrence of the syrinx.

Literature review

The association between DWM and syringomyelia has been reported in 23 subjects [1, 5,6,7,8,9,10,11, 13,14,15,16,17,18,19, 21,22,23]. Among them, nine were reported in autopsy series (Table 1) and 14 in clinical series (Table 2). Only the latter were considered in our literature review, whenever there was direct causal relationship between DWM and syrinx. The syrinx was cervico-thoracic in six [1, 5, 9, 14, 19, 21] and cervical in two cases [6, 18]; in four, the syrinx was extensive (at least 10 myelomers) [5, 14, 19, 21]. A direct communication with the ventricular system was found in five cases [6,7,8], while a CIM-LM was observed in six [5, 9, 14, 18, 19, 21]. Among DWM patients undergoing MRI, neuroimaging findings showed herniation of the lower pole of the posterior fossa cyst through the foramen magnum [5, 6, 9, 14, 18, 19, 21]. The age at diagnosis varied widely from 9 months to 39 years (mean 16.6 years). Most frequent symptoms were headache, especially in the occipital region, and upper extremities sensory-motor alteration [1, 5,6,7, 9, 18]. Regarding the treatment for this condition, many surgical procedures have been used such as sub-occipital decompression with C1 laminectomy and duroplasty [5, 7, 8, 18], cyst decompression and plugging of obex [1], VPS and CPS [5, 9, 19, 21], and syrinx shunting [6]. Globally, postoperative outcome was favorable for all patients with a reduction in size of the syrinx in three patients [5, 9, 21] and complete regression in other three [6, 18, 19]. Among the reports without imaging, clinical improvement was observed in two cases [1, 7].

Table 1 Reported cases of syringomyelia in association with DWM in autopsy series and MRI series
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Table 2 Reported cases of syringomyelia in association with DWM in clinical series
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Discussion

The co-existence of syringomyelia and DWM represents a challenge both for treatment and prognosis and arises interesting questions about the pathogenesis and the best surgical approach.

Mechanisms of spinal cord cavitation

Different possible mechanisms have been proposed to explain the formation of the syrinx in patients with DWM. A first mechanism consists in dilation of a central canal (hydromyelia) anatomically connected to the fourth ventricle. In the presence of hydrocephalus, the impaired CSF circulation out of the fourth ventricle is thought to increase CSF pressure directly on the central canal (communicating syringomyelia). This type of syrinx was found in patients with DWM and Chiari-II malformation and it is also called “fifth-ventricle.” A second mechanism is the impairment of CSF circulation due to obstruction at the level of the foramen magnum, which generates dilation of the central canal that is separated from the fourth ventricle (non-communicating syringomyelia). This type of syrinx was especially associated with Chiari-I malformation (CIM) [2, 12, 17]. Analyzing DWM patients with MRI, the responsible mechanism for syrinx formation was a CIM-like malformation in all cases but one [5, 9, 14, 18, 19, 21]. Also in our case, MRI and intraoperative findings were consistent with an impairment of CSF circulation acting as the abovementioned CIM-like mechanism. Nonetheless, Erdal et al. observed high-flow CSF drainage after syrinx shunting despite a CIM-like mechanism at imaging, thus unveiling that the pathogenic mechanisms might vary across patients and that they cannot be easily identified before surgery.

Treatment

CPS and VPS placement/revision appears to be the treatment of choice in most cases from the 1990s. In fact, decompressing the foramen magnum by either the resolution of the hydrocephalus or the drainage of the posterior fossa cyst or both seem to be appropriate to treat the impaction at this level with a good post-operative outcome [9, 19, 21]. A direct approach to craniovertebral junction by suboccipital decompression with C1-laminectomy and duroplasty was the treatment of choice in the first attempts to treat DWM-associated syringomyelia [1, 7, 8]. Nowadays, it has become a secondary treatment when shunting is ineffective [5]. In our case, size increase and foramen magnum herniation of the posterior cranial fossa cyst was attributed to shunt dysfunction even though supratentorial hydrocephalus appeared stable. Despite intraoperative evidence of distal shunt malfunction, shunt revision showed to be inefficient and direct shunting of the posterior cranial fossa cyst was necessary. According to the literature and the present case, it seems that DWM-associated syringomyelia has a rather complex management and the treatment is still not standardized, often requiring a multicompartimental approach.

Post-operative follow-up

Despite different surgical approaches, the outcome was globally favorable with decrease in size or disappearing of the syrinx at radiological follow-up [5, 6, 9, 18, 19, 21] and/or neurological improvement [1, 7]. A few literature cases and the present report seem to confirm that posterior cranial fossa cyst shunting might represent an effective treatment for DWM-associated syringomyelia and more aggressive treatments should be restrained to cases with no clinical and imaging improvement.

Conclusions

DWM-associated syringomyelia is a rare complication with a poorly understood pathogenesis likely due to CSF circulation impairment. This condition might have a satisfactory outcome but often requires a multicompartimental approach. Longer follow-up studies are necessary to unravel whether ventriculoperitoneal shunt alone or combined with cystoperitoneal shunt can be considered valuable alternative to a more aggressive surgery at the craniocervical junction.