Establishing the Diagnosis

Inherent to surgical intervention, the vast majority of neurosurgical consultations involve diagnostic neuroimaging. In most cases, referral to a neurosurgeon occurs as a consequence of abnormal imaging results, already creating a unique patient-physician relationship. The neurosurgeon is often confronted with the situation of deciding whether the patient’s symptoms or signs, if any, correlate with the neuroimaging findings. This is in stark contrast to neurological practice, in which certain diagnoses such as headache and seizures may not receive diagnostic imaging initially or even at all. Although the finding of a neuroimaging abnormality is not a prerequisite for neurosurgical intervention (such as movement disorder surgery), neuroimaging is required nevertheless (Britz et al., 1995; Kent et al., 1994; and Nijeholt et al., 1998).

The reliance upon diagnostic neuroimaging has changed neurosurgical residency training, necessitating that neurosurgeons achieve a high level of diagnostic neuroradiological competence. For the neurosurgeon, the diagnostic process (and surgical planning) typically hinges upon the imaging, and therefore a considerable amount of time is devoted to carefully, personally reviewing the imaging studies. As a result, when referring a patient for neurosurgical evaluation, it is important to emphasize to the patient that the actual imaging study be physically available for review at the time of the neurosurgical consultation.

It is important to understand the difference between standard diagnostic imaging and the high-resolution neuroimaging required for neurosurgical decision making. For example, routine diagnostic magnetic resonance imaging (MRI) studies of the brain are performed with relatively thick 5-mm slices, with 2.5-mm skip between slices. Although generally adequate to detect lesions 4 mm in size or larger, partial volume averaging can obscure fine anatomical detail such as the relationship of arteries, veins, and cranial nerves to the lesion. For example, although the diagnosis of hydrocephalus may be obvious on routine diagnostic imaging, establishing the etiology of the ventriculomegaly may require high-resolution constructive interference in steady state (CISS) imaging (Fig. 46.1). In this case, a diagnosis of occult aqueductal stenosis would dramatically change the treatment, with endoscopic third ventriculostomy being the preferred treatment rather than a ventriculoperitoneal shunt.

Fig. 46.1 Imaging aqueductal stenosis. Left, Midsagittal noncontrast T1-weighted magnetic resonance image (MRI) showing enlarged lateral ventricle, bowing of corpus callosum, and normal-sized fourth ventricle. Cerebral aqueduct appears patent. Right, Corresponding constructive interference in steady state (CISS) MRI reveals a distal cerebral aqueduct occlusive membrane (white arrow). Premesencephalic cistern has favorable anatomy with a posteriorly placed basilar artery bifurcation (black arrow) for endoscopic third ventriculostomy.

(From Bergsneider, M., Miller, C., Vespa, P.M., et al, 2008. Surgical management of adult hydrocephalus. Neurosurgery 62, 643-660.)

With routine “diagnostic” imaging, the number of different MRI sequences is often limited by the concept of the study being a screening exam rather than one honing in on a certain differential diagnosis. For example, atypical arachnoid cysts can be differentiated from epidermoid cysts if repeat imaging includes a diffusion-weighted imaging (DWI) study (Tsuruda et al., 1990). In this case, an arachnoid cyst may not require referral to a neurosurgeon, whereas the epidermoid cyst should. Consultation with a neuroradiologist, if needed, could lead to proper imaging studies being performed prior to possible neurosurgical consultation.

In other cases, routine diagnostic imaging may be adequate for establishing a diagnosis but inadequate for neurosurgical decision making. In some cases, additional imaging modalities may be required, such as computed tomography (CT) imaging of bony anatomy to supplement abnormal soft-tissue findings on MRI. In other cases, special high-resolution or unique imaging sequences may be required (Barnett et al., 1993; Curtin and Hirsch, 1992). Although beyond the scope of this chapter, suffice it to state that a brief discussion with the neurosurgeon—prior to referral—may in some cases lead to essential imaging studies being obtained prior to the consultation. This may make for a much more productive and useful consultation, obviating the need to have the patient return for an otherwise unnecessary follow-up visit owing to the lack of key imaging studies at the first visit.

Patient Selection for Surgery

Patient selection for surgery is under the purview of the neurosurgeon in most cases, although for many disorders, the neurologist plays an integral and key role. As noted previously, the increasing sophistication and complexity of surgical intervention mandates intimate collaboration between neurologists, neurosurgeons, and other subspecialists. Knowing when to refer to multidisciplinary specialty centers is obviously a function of patient diagnosis and proximity to such centers. In general, community neurosurgeons are well versed in treating a wide range of neurosurgical disorders, although increasingly, many are limiting their practices to mainly treating spinal disorders. Increasing evidence suggests that for specific diagnoses, surgical outcomes are a function of surgical volume load and experience. For example, dedicated brain tumor neurosurgeons performing over 50 brain tumor operations per year generally have better patient outcomes than those only occasionally performing these surgeries (Cowan et al., 2002; and Cowan et al., 2003; D’Agostino et al., 2009; and Shahlaie et al., 2010). Similar findings have been reported for cerebral aneurysm treatment, epilepsy, movement disorders, and pediatric disorders. Most academic centers and some large group private practices have dedicated subspecialty neurosurgeons (as well as the necessary ancillary team) to comprehensively and optimally manage these patients.

Surgeon experience, however, is only part of the equation. Whereas it is highly possible a community neurosurgeon can perform an adequate surgical removal of a brain tumor, neurosurgeons affiliated with a brain tumor center may be able to offer patients clinical studies they might not otherwise be aware of. For some trials, fresh pathological tissue is required, and therefore the operation has to be performed at the site of the trial. Understanding the practice of the neurosurgeons to whom you routinely refer may therefore indirectly improve the care your patients receive.

Patient selection for surgery has become increasingly complex, and new treatment modalities and alternatives have arisen. Just as surgical volume load and experience varies among neurosurgeons, it may be important that the referring physician understand other important factors in patient selection for surgery. An example is vestibular schwannoma (acoustic neuroma) management. As already noted, surgical experience may play a major role with regard to patient outcome. It is important to recognize, however, that fewer patients are choosing surgery for small acoustic neuromas, and instead are undergoing stereotactic radiosurgery or radiotherapy treatment (Andrews et al., 2001; Flickinger et al., 2001; Lunsford et al., 2005; and Meijer et al., 2000). Referring to a neurosurgeon whose practice is located in an area without focal beam radiation capabilities may inadvertently lead to an emphasis on surgical alternatives. A similar situation exists with intracranial aneurysms, in which endovascular coiling has increasingly become the treatment of choice for selected patients. Typically, high-volume neurovascular surgeons are closely affiliated with (or perform themselves) endovascular treatment, and therefore this issue is a moot point (D’Agostino et al., 2009).

Neurosurgery is increasingly subspecialized (as is neurology), and certain diagnoses may require a higher level of expertise. In addition to skull base tumors and neurovascular disorders, others include intractable epilepsy, adult hydrocephalus, movement disorders, and rare conditions such as colloid cysts. A knowledgeable neurologist making the proper initial referral may be a key factor in outcome.

In some cases, the neurologist is the primary determinant of patient selection for surgical intervention. The management of movement disorders is an obvious example. In only a minority of patients is surgical intervention such as deep brain stimulation appropriate Olanow and Koller, 1998). Referral to a movement disorder neurologist first may be appropriate instead of initial referral to a functional neurosurgeon. Other examples include carotid endarterectomy (versus stenting) and cerebrovascular bypass procedures.

To some extent, patient selection for surgery begins prior to neurosurgical evaluation. There are no hard-and-fast guidelines as to what types of neurological diagnoses should be referred for neurosurgical consultation, but in most cases, the decision to refer for neurosurgical consultation is obvious. Symptomatic patients with obvious abnormalities seen on imaging, such as a large cerebral aneurysm, require neurosurgical consultation. There are other cases, however, that may not require neurosurgical consultation and can be managed well and appropriately by the neurologist. Although it may seem obvious and trite, it is important to understand that a neurosurgical practice is a surgical practice. With the increasing use of neuroimaging in our society, so-called incidentalomas are being noted by radiologists (Fainstein et al., 2004; Molitch, 2008; and Molitch, 2009). In some cases, this has led to reflexive referrals to neurosurgeons based solely on the radiology report, without the personal review of the imaging study. Referral of these nonoperative lesions to the neurosurgeon first raises the expectation of the patient that surgical intervention is advised and/or pending, and second takes up a significant amount of the neurosurgeon’s clinic time explaining why the lesion does not require surgery. Examples follow.

Arachnoid Cyst

The vast majority of arachnoid cysts are small and asymptomatic and consequently, nonsurgical. A typical location is the anterior middle fossa where the anterior temporal lobe is displaced posteriorly (Fig. 46.2). Small arachnoid cysts that do not produce significant mass effect (midline shift, brainstem compression) are rarely a cause of headaches (Pierre-Kahn et al., 1990; Pradilla and Jallo, 2007). If it is equivocal whether the lesion is large enough to warrant surgical intervention, a quick film review by the neurosurgeon is often all that is needed to adequately triage the patient.

Fig. 46.2 Transaxial computed tomography image demonstrating bilateral middle fossa arachnoid cysts. Although there is displacement of anterior temporal lobes, note the absence of clinically relevant mass effect (i.e., no effacement of basal cisterns). In most cases, reassurance and follow-up imaging is all that is needed.

Intervertebral Disk Bulges and Annular Tears

Here, the correlation of neuroimaging findings and neurological symptoms and signs is key (Fujiwara et al., 1999) (Fig. 46.3). Clinically insignificant disk bulges are so common in our aging society that a neurosurgical spine specialist could easily be inundated with nonsurgical consultations, stealing time from a practice tailored to helping appropriately referred patients (Stabler et al., 1996; Stabler et al., 1997). Admittedly, inappropriate patient referral to neurosurgeons for asymptomatic disk bulges is infrequent by neurologists, given their training and understanding of neural anatomy.

Fig. 46.3 Sagittal T2-weighted magnetic resonance imaging of lumbar spine showing a disk bulge at L5-S1 level. Referral to a neurosurgeon (or other spine specialist) would be indicated if corresponding neurological symptoms existed.

In some cases, certain diagnoses may not require immediate neurosurgical referral. A prototypical example is pseudotumor cerebri (idiopathic intracranial hypertension). It is generally accepted that surgical intervention is one of the last treatment options for this condition (Acheson, 2006; Kelman et al., 1992; Rosenberg et al., 1993

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