and neck asymmetry. Bipolar release (i.e., complete release of the mastoid and clavicular attachments) combined with Z plasty of the sternal head has been recommended to avoid this complication.

Musculoskeletal torticollis is rarely be a secondary manifestation of cervical skeletal abnormalities, such as occipitocervical synostosis, Klippel–Feil syndrome, scoliosis, basilar impression, atlanto-axial displacement, Sprengel’s deformity, Grisel’s syndrome (chronic atlanto-axial subluxation resulting from inflammation), and congenital subluxations of cervical disks, clavicle fractures, and brachial plexus injury

(Table 9.2).9,14,105,173,180,196

Systemic Causes of Torticollis

Torticollis is rarely auditory, gastrointestinal, rheumatologic, or psychiatric in origin (Table 9.2). An intermittent unilateral face turn in infancy may be the presenting sign of unilateral deafness.209 An extremely large, intermittent head tilt can be a sign of gastrointestinal disease.165 Sandifer syndrome is a rare disorder in which a child with hiatal hernia and gastroesophageal reflux takes a large head tilt to prevent regurgitation.210 Children with Sandifer syndrome typically have a history of vomiting and are thin. Compensation for pain may necessitate an abnormal head position in a variety of other conditions such as cervical arthritis or mastoiditis.209 Psychiatric patients with no neurologic or systemic disease occasionally assume large head tilts for no apparent reason.105

Head Oscillations

Rhythmical oscillations of the head were once termed head nystagmus. In current usage, a nonsaccadic oscillation of the eyes is designated as nystagmus, while a similar oscillation of the head is often referred to as a tremor.60 However, head nodding can be conceptually viewed as a form of “head nystagmus,” because it represents a central disorder of the cephalomotor control system.38 Its neuro-ophthalmologic intrigue lies primarily in its association with pediatric nystagmus, where it may be compensatory (i.e., serving to reduce the intensity of nystagmus and improve vision) or noncompensatory (i.e., a centrally driven oscillation similar to the nystagmus itself).

Several distinct forms of head nodding can be observed in children (Table 9.3).63 Some are benign, while others provide a decisive clinical clue to a potentially life-threatening neurological or systemic disorder that may be treatable.63 Our rudimentary understanding of the phenomenology of head nodding is exceeded by our ability to identify the underlying neurological or systemic disorders that produce it.

Head Nodding with Nystagmus

In children with head nodding and nystagmus, the pathogenetic interrelationship between the ocular and cervical oscillations depends on the underlying condition. To understand how these oscillations interrelate under pathological circumstances, one must first understand the role of the VOR under normal conditions. In normal individuals, the VOR causes any movement of the head to be accompanied by eye movements that are equal in velocity and opposite in direction to that of the head.151 This reflex serves to stabilize the position of the eyes in space so that the direction of gaze remains constant during head movements. Thus, in children with nystagmus, head nodding would not be expected to change the waveform of nystagmus, because the head movements would be countered by the VOR, leaving the nystagmus to determine the position of the eyes.97 It is now clear, however, that this rule cannot be applied to individuals with congenital nystagmus, because head or total body movements can produce a dynamic shift in the null position (see Chap. 8) and thereby modify the congenital nystagmus waveform.61 The change in the overall congenital nystagmus waveform induced by vestibular stimulation is often misconstrued as evidence of an underlying deficit in the VOR in individuals with congenital nystagmus.

In the child with nystagmus, head oscillations could function to improve vision only if (1) the VOR gain was inherently abnormal, (2) a normal VOR gain was somehow actively suppressed by the head movements, or (3) activation of a normal VOR could somehow “override” the nystagmus. Regardless of any clinically apparent effects of head oscillations

Table 9.3  Head nodding in children: Differential diagnosis

on the overall intensity of congenital nystagmus, compensatory head movements would have to prolong foveation time to improve vision.38,60

Spasmus Nutans

Spasmus nutans is the most common condition associated with head nodding in children.45 The head nodding of spasmus nutans consists of a combination of true (anteroposterior) head nodding and lateral shaking of the head in an unpredictable pattern.107,193 It becomes prominent when the child inspects an object of interest and it seems to increase with the complexity of the fixation target.91,95

Gresty and colleagues95,96 were the first to describe simultaneous eye and head movement recordings in three children with spasmus nutans in whom head nodding abolished the nystagmus, activated normal VORs, and suppressed the nystagmus. These children had better vision when they nodded their heads. Gresty and colleagues concluded that the head nodding was an operant-conditioned phenomenon that served to suppress the nystagmus and improve visual acuity, and not a separate pathological phenomenon.

Gottlob et al91 analyzed simultaneous head and eye movement recordings in 35 children with spasmus nutans. In 21 of these patients, the fine, fast dissociated nystagmus changed during head nodding to larger and slower symmetrical eye movements, with both eyes oscillating in phase at the same amplitude and 180 degrees out of phase to the head movements (see Fig. 8.8). The ocular oscillations during head nodding corresponded to a normal VOR. These investigators concurred with Gresty and colleagues95,96 that head nodding in spasmus nutans is an adaptive strategy to improve vision rather than an involuntary movement of pathological origin. Head nodding in spasmus nutans must therefore reduce or abolish the nystagmus through a mechanism that functions independently of the VOR or through stimulation of the powerful VOR to override the nystagmus.198

Gottlob et al91 also found that passive horizontal shaking of the patient’s head by the examiner suppressed mainly the horizontal nystagmus, whereas passive vertical shaking suppressed mainly the vertical nystagmus. This finding suggests that the principle direction of the head nodding in spasmus nutans may be dictated by the trajectory of the nystagmus. The associated head tilt in spasmus nutans may help directionalize the head nodding to most effectively suppress the nystagmus.91 Because children with spasmus nutans often utilize rapid elliptical or “figure eight” head movements when viewing objects of interest, the mechanism by which these head movements serve to improve vision may be more complex. Gresty and Halmagyi97 questioned whether a child’s ability to cancel nystagmus and improve vision by shaking the head (as seen almost exclu-

sively in spasmus nutans) could be construed as a predictive neurodevelopmental sign that the nystagmus would eventually resolve. Whether the eventual disappearance of spasmus nutans requires active suppression or it represents recovery of maturation ocular stabilization systems is unclear.

Infantile Nystagmus

Approximately 10% of individuals with infantile nystagmus display a rapid, horizontal, pendular shaking of the head.79,160 According to Jan et al117, this head shaking occurs in bursts of 5–30 s and only during intense visual fixation. It occurs only with visual activity and does not involve any other part of the body. Head nodding in infantile nystagmus is a subconscious act that ceases when it is called to the individual’s attention and cannot be willfully reactivated.117

Many of the early conclusions drawn from studies pertaining to the interrelationship of infantile nystagmus and head shaking were based on clinical observations regarding the overall waveform of the nystagmus without objective documentation of the effect of head shaking on foveation periods. For many years, head shaking in infantile nystagmus has been thought to be compensatory in nature.46 This idea was attractive, because it seemed consistent with the clinical observation that the head nodding increased noticeably during periods of fatigue, anxiety, and intense curiosity, when the intensity of the nystagmus also increased.117 Electro-oculographic studies claiming to show that the VOR was defective in infantile nystagmus (see Chap. 8) seemed to provide a pathophysiological basis for the notion that head oscillations could stabilize the position of the eyes in space without being neutralized by a normal VOR.

These early studies were inherently flawed either in premise or implementation. Some investigators provided only verbal descriptions of infantile nystagmus in which the head oscillations appeared to be equal and opposite to the ongoing eye movements (with a VOR gain somehow reduced to zero) or in which the head oscillations seemed to cancel the ocular oscillations by a central mechanism, as in spasmus nutans, without providing simultaneous eye and head movement recordings to support these claims.96,97 One report contained simultaneous head and eye movement recordings, but showed jerky head movements of approximately 30 degrees that were supposedly compensating for a nystagmus of approximately 7 degrees.150 In another case, eye movement recordings showed convergent nystagmus (which is consistent with spasmus nutans but not with infantile nystagmus) and head movements that canceled the nystagmus.198 As with smooth pursuit, the sustained vestibular input from head nodding produces a dynamic shift in the null zone, which changes the overall waveform of the nystagmus. The failure