Once the diagnosis of adult Chiari is made, treatment options include observation versus surgical intervention depending on the severity of symptoms and the presence or absence of syringomyelia. The goal of surgery is to normalize the flow of cerebrospinal fluid around the brainstem and cerebellum at the foramen magnum. This is usually accomplished by performing a midline suboccipital craniectomy and duraplasty. Posterior cervical laminectomies of C1, and occasionally C2 or lower, may be necessary to fully expose the descended cerebellar tonsils. Duraplasty may be performed with a dural substitute such as bovine pericardium or DuraGen or with autograft such as local pericranium or fascia lata. Surgical complications include leakage from the wound, shunt-requiring hydrocephalus, infection, aseptic meningitis, subdural hematoma, and respiratory depression. Complication rates range from 10 to 33 % depending on the series. Substantive and lasting improvement is generally in the 80–90 % range [28–30].

Clearly Chiari 1 malformation is a complex syndrome with still poorly understood pathophysiology. The multiplicity of presenting complaints, poor correlation with radiographic findings, and high surgical complication rates make it a formidable disease process. However, with careful patient selection and meticulous attention to surgical detail, Chiari 1 treatment can be extremely gratifying.

Normal pressure hydrocephalus (NPH) is an acquired diagnosis, usually seen in an older population. Similar to Chiari 1, it involves a disruption of cerebrospinal fluid flow dynamics. The classic triad of NPH includes dementia, gait disturbance, and urinary incontinence. NPH is an important diagnosis to evaluate in the setting of memory and cognitive impairment because it represents a remediable form of dementia. Many neurologic conditions, most commonly Alzheimer’s dementia and Parkinson’s disease, may present with symptoms similar to NPH. In addition, multiple other disease states can have similar findings please see Table 6.2 [31]. The gait disturbance of NPH is usually the first symptom to present and often manifests as short, shuffling, unsteady steps. Because of the perceived difficulty of lifting one’s feet off the floor, this gait is often described as “magnetic.” Dementia presents with impaired memory with both bradyphrenia (slowness of thought) and bradykinesia (slowness of movement). Urinary incontinence is usually a later symptom and completely unwitting by the patient.

Because NPH shares signs and symptoms with so many disease states and has a poorly understood pathophysiology, it is difficult to diagnose. A good clinical history detailing the above symptoms presenting insidiously and progressively is important. Ventriculomegaly out of proportion to overall atrophy on CT or MR imaging is also useful but not a solely diagnostic criterion. A “tap test” or high-volume lumbar puncture is often performed. Opening pressures are generally in the upper range of normal (15 ± 4.5 cm H₂O) and 40–50 ml of CSF removed [31]. Many centers prefer a trial of ambulatory lumbar drainage in which a lumbar drain is inserted and CSF drained constantly for 3–5 days. Patients will often experience an improvement by day three and a slow relapse after the drain is removed. Radionuclide cisternography and cerebral blood flow measurement testing rarely yield helpful diagnostic information.

Once the diagnosis is established, CSF diversion is the treatment of choice. This can be performed with a lumbar-peritoneal shunt or more commonly with a ventriculoperitoneal shunt. Generally programmable shunt valves are employed in order to glean the most benefit from CSF diversion without exposing the patient to undue risk. A retrospective review of shunt insertion for NPH estimated a complication rate between 34 and 57 %, though this included long-term follow-up inclusive of delayed shunt malfunctions [32]. These complications included subdural hematoma, intracerebral hematoma, infection, seizure, and shunt malfunction. Estimated mortality directly associated with shunt insertion for NPH is 2 % [33].

Unlike most procedures where the risk is directly around the time of surgery, the risk of subdural hematoma is increased for the remaining lifetime of the patient, given the shunt is in good working order. As the usually enlarged ventricles are slowly drained and shrink, the mantle (tissue from the cortex or surface of the brain to the ventricular wall) may not proportionally expand. This makes the cortex more likely to sag away from the dural lining of the skull. The surface cortical veins are thus put on stretch and are more likely to rupture, resulting in a subdural hematoma. Moreover, as blood collects in the subdural space, placing pressure on the brain, the shunt will allow the ventricular system to further decompress, encouraging the hematoma to expand. Despite the relatively high reported morbidity and mortality rates associated with shunt insertion for NPH, most patients, and their families, opt for the procedure given the alternative bleak prognosis as well as the often near complete reversal of neurologic decline.

Chiari 1 and NPH represent two diagnoses relevant to the care of adults with neurologic deficits. They are both remediable disease processes, at least for a given amount of time, but if missed subject patients to a lifetime of progressive issues. However, with proper diagnosis and treatment, both Chiari 1 and NPH are extremely responsive to neurosurgical intervention instilling meaningful positive impact on lives of both patients and their families (Tables 6.1 and 6.2).