Troubled History in “The Year Nineteen Thirteen

Perseverance is required to diagnose cranial nerve injury in the presence of severe head trauma.⁴⁹ Coma may obscure all but cranial nerve III, VI, and VII damage.⁵⁹ Diagnosis of trochlear nerve injury in particular requires a high level of patient coop-eration.⁵⁴ Injury to the orbital muscles may be im-possible to distinguish from ocular motor nerve damage. Loss of smell from nasal obstruction may be confused with olfactory nerve damage, and blockage of the auditory canal or damage to the middle ear may be difficult to distinguish from nerve VIII interruption. Craniofacial and skull base fracture can be overlooked while treating more life-threatening injuries.⁴²

Head trauma is a recurrent event. As with strokes, the greatest risk factor is a similar previous experi-ence. Memory falters with successive blows to the head, alcohol further dulls recollection, and the possibility of previous unacknowledged injuries must be kept in mind. Cranial nerve signs may be old, the frozen eye may be prosthetic rather than paralyzed, and even the bullet seen on head scans may be old and incidental. With motorcyclists in particular, only death or multiple dismemberment

dampens the ardor for repeat encounters with large objects.⁵⁵

Neurological disabilities are often linked in pa-tients’ minds to recent episodes of trauma. If the connection seems unlikely, it probably is. Even when head injury is the immediate cause of cra-nial neuropathy, an underlying problem may be present. Trivial blows resulting in surprising pal-sies to cranial nerves III or IV or lower cranial nerves may be acting on nerves already compro-mised by tumor.²²

Which Nerves Are Injured Most Commonly?

The exact incidence of damage to each cranial nerve varies with patient selection and length of follow-up (Table 6.1)18,24a,24b,25,30,39,87,91,103 There is general agreement that the olfactory and facial nerves and audiovestibular function are damaged most often by blunt head injury. Trauma to the optic nerve and each of the ocular motor nerves is intermediate in frequency, whereas the trigeminal nerve trunk and the lower cranial nerves are rarely injured.

Delayed Signs

The facial nerve may appear normal initially and then develop weakness several days after head injury. Delayed nerve VI palsies are usually due to increased intracranial pressure or hemorrhagic meningitis. Late appearance of oculomotor nerve paresis, even without pupillary involvement,⁴⁵ is a more ominous sign indicating transtentorial herniation. Tentorial herniation is not a cause of trochlear or abducens damage. Rarely, damage to intracranial arteries can result in delayed cranial neuropathies owing to aneurysm forma-tion.³⁷ Serial follow-up evaluations are necessary therefore to fully evaluate cranial nerve trauma (Fig. 6.1).

Type of Injury

Cranial nerve findings can predict the type of head injury. Gunshot trajectories among survivors show-ing cranial nerve damage follow two general paths:

In many suicide and some homicide attempts, an entry wound in front of the ear takes a transverse path that results in blindness. Eye movement limi-tation is common, but brain damage may be mini-mal.⁵⁰ Such cases have been reported regularly since the introduction of radiographs; Cushing published one of the more dramatic illustrations (Fig. 6.2).¹³ More common in homicide attempts is an infraorbital entry with a downward path to either side of the neck, sparing the brain but dam-aging the lower cranial nerves and frequently the carotid artery and the sympathetic trunk. Facial paralysis and deafness are more common with missile injury to the temporal bone than following blunt trauma.⁸⁴

Table 6.1. Percentage of Patients with Traumatic Damage to Each Cranial Nerve

Reference No. of

No. Patients I II III IV V VI VII IX, X

22 430 2.6 — — 0.1 0.2 0.4 1.6 —

27 1285 3.0 — 0.5 — — 0.4 2.9 0.16

35 1800 0.5 4.0 4.0 1.4 3.6 4.1 4.7 0.05

75* 291 14.0 2.7 6.6 — — 2.7 3.0 —

91 1550 7.7 1.8 1.0 1.0 1.0 1.0 3.0 0.06

*Limited to severe head injury.

With blunt head injuries, many middle and lower traumatic cranial neuropathies are accompanied by basilar fractures. All cranial nerves (except IX to XII) are at risk, but the olfactory nerve and the facial nerve are most commonly injured.⁶⁹ Sym-metric middle cranial neuropathies often result from skull-crushing injuries,⁹⁹ such as happens when an automobile slips off the jack onto the mechanic’s head. This pressure cracks the skull like an egg, stretching the nerves but sparing the brain (Fig. 6.3). Hyperextension neck injuries may selectively interrupt cranial nerves VI and XII bilaterally, but associated direct damage to the pontomedullary junction or indirect brain stem infarction following vertebral artery injury may obscure cranial nerve damage.⁵¹

Stretching injuries tend to damage nerves at fixed attachments or at points of sharp angulation.

Autopsy reports come largely from coroners’ of-fices and emphasize rapidly fatal injuries. The high frequency with which nerves are pulled loose from the brain stem in these reports reflects the severe forces involved and provides an explanation for failure of recovery in more than half of traumatic cranial neuropathies.³⁴ The optic nerve is a some-what special case. It is tethered within the optic canal—the usual site of injury—and is subject to stretching with brain shifts. In addition, however, the bony architecture of the orbit directly transfers force from the superolateral orbital rim to the optic nerve canal.²⁸

Terrorist bomb attacks are an increasingly com-mon cause of cranial nerve injuries in civilians.⁶⁷ Cranial nerves VII and VIII are particularly vulner-able to shrapnel penetrating the temporal bone.

The examining physician must be alert to small skin imperfections around the ear canal to identify pen-etrating wounds.

Posttraumatic Cranial Neuropathies 131

Recovery

It is uncertain how often, how soon, and how well patients recover from traumatic cranial neuro-pathies. Follow-ups are notoriously poor in this group. When patients do return, the average phy-sician will skip the olfactory nerve, be casual about testing vision and hearing, and record aberrant regeneration of nerve III as recovery. Chances of return of function vary with the nerve involved:

The facial nerve usually recovers, the ocular motor nerves return to normal about 40% of the time,⁹⁰ and the first two cranial nerves show significant improvement in less than one-third of cases.^38,101 Lesions of the audiovestibular nerve are usually permanent.

Treatment

There are few situations in which any therapy is of unequivocal benefit in restoring cranial nerve func-tion after traumatic injury. In particular, strong opinions concerning treatment of optic nerve dam-age generate heat rather than light. Various mea-sures have been advocated after injury to cranial nerves II through VIII and are discussed in those sections.

Figure 6.1. Vagaries of trauma are illustrated by a patient who was stabbed at the inner canthus of the left eye (A—top) by a ballpoint pen that penetrated the skull (B) but spared the medial rectus muscle, cranial nerves, and carotid artery. Left medial rectus weakness (A—

bottom) was seen 2 years later when he returned with internuclear ophthalmoplegia as the presenting sign of multiple sclerosis.

(B) (A)

Figure 6.2. An awake patient with blindness fol-lowing gunshot wound in a suicide attempt. Source:

Cushing.¹³

Olfactory Nerve

Medical students and house officers increasingly begin their cranial nerve examination with vision, as in “cranial nerves II through XII intact.” This neglect in testing the sense of smell transfers to the patient the burden of detecting a loss of taste and smell.¹⁶ Of all patient complaints of loss of smell at a “nasal dysfunction clinic,” 10% were related to trauma, and two-thirds had inflammatory/viral causes.¹⁵

Anosmia is more common with occipital than with frontal blows and can result from trauma to any part of the head. Recovery occurs in more than one-third of cases, usually during the first 3 months. Some patients, however, are reported to show improve-ment as late as 5 years after injury. Trivial blows can

cause permanent loss of smell, but the incidence of anosmia parallels the severity of head trauma. A high percentage of patients with posttraumatic olfactory dysfunction (88%) show abnormalities in the olfac-tory bulbs and tracts and the inferior frontal lobes on magnetic resonance imaging (MRI).¹⁰⁴

Sumner extensively reviewed previous studies¹⁰⁰ and credited Hughlings Jackson with the first re-port of posttraumatic anosmia in 1864. Most stud-ies agree that the olfactory nerve is the cranial nerve most often damaged by blunt head trauma. Leigh⁷¹ found anosmia in 5.0% of patients with head inju-ries, Turner^103a in 7.7%, Hughes³⁹ in 10.5%, Fried-man and Merritt²⁵ in 2.5%, Sumner¹⁰⁰ in 7.1%, and Zusho¹⁰⁵ in 4.2%. Sumner suggests an overall cidence of 7%, rising to 30% with severe head in-juries or anterior fossa fractures.¹⁰¹

Optic Nerve

Clinical Presentation

Type of Injury

About one-fourth of civilian optic nerve trauma is due to penetrating injury (Table 6.2). Gunshot wounds are the usual cause, with orbital perforating injuries and surgical complications being less com-mon. American men strongly prefer handguns for suicide. The usual technique of holding the muzzle to the temple frequently destroys both optic nerves, but even less common methods such as positioning the muzzle beneath the chin or “swallowing the bar-rel” may produce blindness in one or both eyes.⁵⁰ Indirect optic nerve injury results from trauma to the ipsilateral outer eyebrow with astonishing regularity. Forces exerted there are transmitted Figure 6.3. Patient following crush injury to the skull

looking left (top) and showing one (of two) nerve VI palsies: closing the eyes (center), showing bilateral nerve VII pareses; and computed tomography (bottom) illustrating pneumocephalus accompanied by a subjec-tive splashing sound with head movement.

Table 6.2. Traumatic Optic Nerve Injuries*

Blunt injury 191

Unilateral 150 (78%)

Bilateral 22 (12%)

Chiasmal 19 (10%)

Penetrating injury 53

Unilateral 44 (83%)

Bilateral 8 (15%)

Chiasmal 1 (2%)

*Inpatients seen at the Los Angeles County/

University of Southern California Medical Center over 24 years.

Posttraumatic Cranial Neuropathies 133 directly to the optic nerve canal,^6b,28 the usual site

of traumatic optic neuropathy.^12,75 Occasionally, temporal-parietal blows will damage the optic nerve, but occipital trauma rarely produces optic neuropathy. In a few patients, injuries to the globe result in avulsion of the optic nerve, with associ-ated fundus hemorrhage and disruption.^3a Rarer still are the psychotic individuals who heed the advice given by the apostle Matthew: “If thy right eye offend thee, pluck it out.”⁶⁸ Removal of an eye and the attached optic nerve is a relatively simple procedure for the motivated, and unfortunately, many self-enucleations are bilateral.

The optic nerves, like the olfactory and trochlear nerves, can be damaged by trivial blows, but most traumatic optic neuropathies are associated with severe head injury with unconsciousness. (In the horse, unconsciousness rarely accompanies such injuries.⁷⁸) On a neurosurgery service, optic nerve damage tends to be severe and the diagnosis de-layed. Restoration of vision is unlikely, and prece-dence is naturally given to protecting life and brain function. Emergency room patients in whom mo-nocular visual loss is the chief complaint have in-juries that are milder and often isolated. In such cases, diagnosis and treatment should be prompt.

Visual Loss

The most common result of optic nerve injury is complete blindness in one eye, but any degree of

impairment of visual acuity may occur.15,63,66,72

Similarly with partial damage, any type of visual field loss may occur, but inferior altitudinal defects are relatively frequent. About 10% of patients will show signs of bilateral optic nerve or chiasmal dam-age (Fig. 6.4),⁹³ usually in association with severe head injuries. Many chiasmal lesions are asymmet-ric, with unilateral severe optic neuropathy asso-ciated with contralateral temporal hemianopia.

Occasionally, a patient will present with spuri-ous visual loss after head trauma. If that possibil-ity is kept in mind, the diagnosis is not difficult.⁵¹ The usual picture is that of monocular blindness or severe monocular visual loss accompanied by a tunnel field or spurious hemianopia.⁶⁰ Lack of an afferent pupillary defect confirms the diagnosis of functional visual loss, and a firm, optimistic prog-nosis should be rendered.

Indirect optic nerve trauma usually produces immediate visual loss. Spontaneous improvement is rarely documented in an inpatient neurosurgi-cal setting but may occur in more than one-third of patients in more favorable situations.^37,63,93 The presence of blood within the posterior ethmoid cells, age over 40 years, loss of consciousness with the traumatic optic neuropathy, and absence of recovery after 48 hours of steroid treatment are all poor prognostic factors for recovery of vision.¹¹

Delayed visual loss is potentially reversible. A small percentage of patients develop progressive

Figure 6.4. Patient with damage to the chiasm, left nerve III, and bilateral nerves VI following blunt head injury.

visual loss several hours to several days after injury, presumably owing to edema or ischemia within the canal or compression from an evolving orbital sub-periosteal hematoma.^24c Rarer still is a delay of days to weeks resulting from enlargement of traumatic mucoceles⁷⁰ or posttraumatic aneurysms.⁴⁴

Evaluation

Clinical evaluation of the conscious patient consists of prompt testing of visual acuity and fields and using the swinging flashlight test to search for an afferent pupillary defect. In the unresponsive pa-tient, evaluation depends on afferent pupillary function, and the frequent association of efferent pupillary damage may make this a difficult task.

Although early optic disk pallor does not appear until 1 month after injury, funduscopy is necessary to rule out vitreous or retinal hemorrhage as the cause of visual loss.

Radiographic and laboratory testing are of limited value in the presence of immediate visual loss. Frac-tures through the optic canal can be demonstrated in about one-half of such patients, but this finding is of limited practical concern. Small optic nerve sheath hematomas occasionally accompany optic nerve injuries. Similar sheath hemorrhages are fre-quently seen with subarachnoid hemorrhage and other acute intracranial bleeding,⁴⁶ where they do not interfere with vision. Their presence after head trauma is expected, will rarely be a factor in visual loss, and should not overly excite the surgeon.

Treatment

There is agreement that prompt treatment is im-perative in cases of delayed visual loss. The effec-tiveness of treating immediate injuries remains unproven. The optic nerve and the spinal cord are similar in being central nervous system tracts con-tained within bony canals, and effective therapy for one may well benefit the other. Evidence that im-mediate high-dose steroid therapy results in an improved outcome after spinal cord injuries⁷ is a strong recommendation for its prompt use in nearly all cases of traumatic optic neuropathy. The dangers of fluid rhinorrhea must be weighed against potential benefit to the optic nerve.

Continuing the analogy to the spinal cord in the case of surgery, which has proven of little benefit in stable spinal cord injuries, is not encouraging for

the role of surgical decompression of the trauma-tized canicular optic nerve. In practice, however, favorable results of decompression have been reported with increasing frequency and enthusi-asm.26,74,76,81,98,102 (These reports should be tem-pered by recalling the decade of perfervid testimonial to the efficacy of decompression in Bell’s palsy.) Unfortunately, definitive studies do not exist. The International Optic Nerve Trauma Study was inconclusive because of the limited num-ber of eligible patients.⁷³ A recent prospective non-random study of steroids and endoscopic optic nerve decompression showed visual improvement in 70% of patients treated within 7 days of injury compared to only 24% of patients treated after 7 days.^86a However, in patients who are not com-pletely blind, improvement can occur even when surgery is undertaken a few months after injury.⁶²

Ocular Motor Nerves (III, IV, AND VI) Clinical Presentation

Nerve III

The dilated pupil and turned-out eye of a patient with a major nerve III palsy provide a distinctive appearance even in the unconscious patient.⁵⁸ The principal temptation is overdiagnosis of oculomo-tor nerve paresis in the face of concomitant orbital trauma. A fixed, dilated pupil after face and head trauma commonly represents traumatic mydriasis owing to iris injury or orbital parasympathetic dam-age. Distinguishing nerve III damage from diffuse orbital muscle limitation depends on relative

spar-Table 6.3. Ocular Motor Nerve Palsies*

Number Number

as a as a Percent

Nerve Affected Result of Result of Due to

Trauma All Causes Trauma Trauma

Nerve III

Direct trauma 197 843 23

Herniation 128 —

Nerve IV (bilateral 35) 116 185 63 Nerve VI (bilateral 65) 181 889 20 Total III-IV-VI palsies 494 1917 26

*Inpatients seen at the Los Angeles County/University of Southern California Medical Center over 24 years.

Posttraumatic Cranial Neuropathies 135 may even be confused with each other in a stupor-ous patient who exhibits esotropia on downward gaze.

Rarely, apparent bilateral nerve VI palsies will vary dramatically from moment to moment. This inconsistency raises the possibility of voluntary con-vergence spasm. Observing that miosis occurs in proportion to esotropia will establish the diagnosis.⁴⁸

Diagnostic Tests

Recorded diplopia fields (Lancaster or others) are useful for diagnosis and follow-up of cooperative patients with minimal diplopia. A computed tomog-raphy (CT) scan is automatic after any significant head trauma. The formerly paramount question concerning whether a nerve III palsy was immedi-ate and due to direct trauma or delayed and due to tentorial herniation is now answered before it arises. One surprise with scanning has been the unexpectedly high incidence of dorsolateral mid-brain contusion with trochlear palsy.²⁶ Computed tomography and MRI scans are highly useful in sorting out the cause of delayed diplopia. Slowly evolving tentorial herniation may be subtle and carries high mortality and morbidity even in the scan era.45,47,53,60

Treatment

Initial treatment of diplopia consists of patching for comfort. Most patients will choose to patch the more limited eye, and it is not necessary for adults to alternate the patch. Some patients with trochlear palsies will prefer to achieve single vision by tilt-ing the head and tucktilt-ing the chin down. Overall, about one patient in five will find a patch more nuisance than help. Like hospital gowns, eye patches of unusual cheapness seem to appeal to hospital administrators. A decent patch should be comfortably convex, with sufficient elastic to avoid secondary glaucoma. Patients who experience diplopia only in a small field of vision can apply semitransparent tape to the appropriate portion of one lens of their glasses for a better cosmetic and functional result.

Paste-on prisms, combined with considerable patience by both physician and patient, may occa-sionally improve the area of binocular single vision.

Injection of botulinum toxin into the antagonists of paralyzed muscles is a technique that promises ing of lateral movement and may need to await

reduction in orbital swelling. Infraorbital numb-ness suggests an orbital blowout fracture and ar-gues against a nerve III palsy.

A fracture through the orbital roof is much less common than a floor fracture and is even more important to diagnose promptly⁵⁷; the accompany-ing subfrontal hematomas may require emergency neurosurgery.^86b Roof fracture often mimics supe-rior division palsies of nerve III (Fig. 6.5). The leva-tor and superior rectus muscles are paralyzed, but in these cases, damage is due to direct muscle in-jury by “blow-in” bone fragments or hemorrhage.

Recovery of oculomotor nerve function more than 6 weeks after trauma, with disproportionate improvement in adduction and highly variable

Recovery of oculomotor nerve function more than 6 weeks after trauma, with disproportionate improvement in adduction and highly variable