Resonance Disorders

John E. Riski, Ph.D.


Hypernasality is often incorrectly mislabeled as a voice disorder. Voice disorders are caused by dysfunction of the larynx. Hypernasality and nasal air flow disorders are caused by a dysfunction of the velopharyngeal mechanism.

Speech therapy for voice disorders involves voice re-education and vocal hygiene programs. Speech therapy for mild hypernasality involves articulation therapy techniques. Hypernasality often requires physical management, such as surgery or prosthetics.

Medical management for voice disorders is by otolaryngologists (ear, nose and throat specialists) and surgical management for hypernasality is by a plastic surgeon or craniofacial surgeon who participates on a cleft palate-craniofacial team.

Velopharyngeal Incompetence (VPI)

Velopharyngeal incompetence or VPI is the inability of the velum (soft palate) and related musculature to close the nasopharynx, separating the oral and nasal cavities for the production of oral consonants. A VPI can be caused by a deficiency of the velum or an increased size of the pharynx. The latter is difficult to diagnose without imaging.

A VPI usually has a physiological origin and requires physical management such as surgery or prosthesis. A VPI might also be a sound substitution. It is now more correctly referred to as a "nasal snort”. The hallmarks are nasal air escape only on specific sounds, usually the sibilant sounds, "s, z", normal resonance and no nasal air escape on other consonant (plosive) sounds. Oral air flow for "s" can usually be taught easily. Since this is a sound substitution it requires speech therapy. Surgery is unwarranted.

An unwarranted VPI might also be considered when the nasopharynx is obstructed and cannot open adequately for breathing and producing the three nasal consonants (resulting in hyponasality). The cause may be hypertrophied adenoids, aggressive pharyngoplasty or narrowed nasopharynx from other causes. This is difficult to diagnose without imaging.

What are possible symptoms of VPI?

  • Hypernasality
  • Hyponasality
  • Nasal air escape
  • Reduced oral pressure for consonants
  • Compensatory Articulation including:
    — Glottal stops
    — Pharyngeal fricatives
    — Nasal snorts (more correctly labeled posterior nasal fricatives)
  •   Velopharyngeal function is the functional relationship between the velopharyngeal musculature and the pharyngeal space. Both should be evaluated.

What causes resonance disorders?

The primary causes of hypernasality are structural deficits, neurological disorders and faulty learning.

Structural deficits include:

Cleft Palate (with or without cleft lip) — These are usually easy to identify. The presence of a cleft palate identifies someone who has an increased chance of hypernasal speech.

  • There is approximately a 20% incidence of hypernasality after initial palate closure.
  • The role of the speech pathologist is to identify these children ASAP!
  • Earlier treatment of VPI seems to allow for better overall speech.
  • Large VPIs are treated early; borderline VPIs are treated later.

Submucous Cleft Palate — This is often more difficult to identify. The most obvious forms include a bifid uvula, intact mucosa but noticeable separation of muscle in the midline of the soft palate, and absent posterior nasal spine of the hard palate with obvious forward attachment of the soft palate muscles. The less obvious forms can only be detected only by identifying anterior levator attachment, measuring the thickness of the soft palate on radiographic studies or the continuity of muscle on the nasal surface of the soft palate by endoscopic examination.

Deep Pharynx — This is the most difficult to recognize since the deficit is in the size of the nasopharynx and not of the soft palate. The soft palate may appear normal by oral exam. The velopharyngeal deficit can be identified only by lateral radiographs or lateral fluoroscopy. The primary features are the speech characteristics of hypernasal resonance, nasal air escape and possibly “cleft palate-like misarticulations” without obvious physical deficits. Other characteristics are nasal regurgitation as a newborn, difficulty nursing and delayed, hypernasal speech with normal language development. The speech-language pathologist is extremely important in the ultimate diagnosis and referral for appropriate evaluation and management of disorders of the deep pharynx. Hypernasality and speech deficits are the primary characteristics.

  • VPI is often not diagnosed or diagnosed late because the palate appears normal and the pharynx is not evaluated.
  • When diagnosed after speech has begun, sparse adenoid mass may be a factor.
  • Hypernasality is the primary presenting factor.
  • Hypernasality may be present from onset of speech — some children do not grow adenoids.
  • After adenoidectomy — deep nasopharynx is unmasked (velo-pharyngeal mechanism seems able to adjust to slow involution but not the sudden increase with adenoidectomy).

Neurological causes or dysarthrias include:

Upper Motor Lesions

Upper motor deficits are caused by head injury, cortical stroke, cerebral palsy, brain tumors or irradiation. In this “spastic dysarthria,” all speech subsystems (respiration, laryngeal, velopharyngeal and articulatory) may be affected to some degree. These may lead to a “spastic weakness” of the speech mechanism including the velopharyngeal mechanism. Deficits are bilateral and characterized by increased muscular tone. Instrumental evaluation is helpful to measure the function of each subsystem and its contribution to the overall speech deficit.

  • Spasticity and increased tone are the chief characteristics (spastic weakness).
  • May be congenital or adventitious (cerebral palsy or trauma).
  • Deficits are bilateral.
  • Hypernasality may be accompanied by harsh (spastic quality) voice quality.
  • There may be a vocal tremor.

Lower Motor Lesions

Lower motor deficits such as lesions to the Xth (Vagus) cranial nerve, isolated lesions to the pharyngeal branch of the Vagus, or brainstem stroke or tumor can cause a flaccid dysarthria characterized by decreased muscular tone. Isolated cranial nerve deficits cause unilateral muscular deficits. When the lesion to the Vagus is above the pharyngeal branch, the soft palate and larynx will demonstrate deficits on the same side and the resulting speech will be hypernasal and breathy. A brainstem stroke or tumor may affect more than one cranial nerve.

  • Flaccidity and atrophy are the major characteristics.
  • May be congenital as in Moebius Syndrome.
  • May be adventitious as in surgical or accidental trauma to peripheral nervous system.
  • Deficits are usually unilateral. Both the larynx and velum should be checked if one is paralyzed.

Faulty Learning: Functional VPI or Sound/Specific VPI

Faulty learning is not truly a velopharyngeal deficit, but rather represents a unique sound substitution.

The terms Functional VPI and Sound/Specific VPI have been used in the literature to label this disorder. A Functional VPI can be confusing to diagnose because it presents with nasal air escape just as structural and neurologic deficits. The nasal air escape is caused by constricting the velum against the posterior pharyngeal wall while the tongue stops oral air flow. This sound substitution was previously labeled a nasal snort. The physiology of this substitution is now better understood and more appropriately labeled a posterior nasal fricative. It is usually substituted for the sibilant (“s” and “z”) and affricate (“ch” and “dg”) sounds.

  • Since velopharyngeal function is normal, the stop-plosives do not have nasal air escape and resonance is normal.
  • The velum is neurologically and anatomically capable of closure at the time of evaluation.
  • The most plausible theory is that this develops as a compensation to early (first year of life) conductive hearing loss. The sound “s” is a very soft sound and the child cannot hear it with even a small conductive hearing loss. In contrast the “posterior nasal fricative” creates a bone conducted signal that is transmitted up the cervical spine to the skull and inner ear bypassing the conductive loss.
  • Will not respond to surgery or prosthetic management. Requires speech therapy.

What kinds of patients benefit from an instrumental evaluation of speech disorders?

Patients with the following diagnoses may benefit from instrumental assessment:

  • Cleft palate
  • Craniofacial and related disorders
  • Dysarthria
  • Traumatic brain injury
  • Brain tumor
  • Neurologic disease
  • Cerebral palsy
  • Congenital or acquired anomalies
  • Voice disorders

What kinds of speech symptoms are heard in these patients?

Patients may present with a number of symptoms including:

  • Hypernasality and/or nasal air escape (cleft palate, post tonsillectomy/adenoidectomy, neuromotor disorder — acquired or congenital)
  • Hyponasality (nasal or nasopharyngeal obstruction)
  • Articulation (glottal stops or pharyngeal fricatives)
  • Swallowing disorders
  • Hoarseness
  • Dysarthria
  • Poor response to speech therapy
  • Difficult-to-diagnose speech problems

What computer-based instruments are used to analyze speech?

  • Pressure flow
  • Nasometry
  • Acoustic analysis instruments

How can instrumentation and imaging help with speech disorders?

They improve understanding of voice and resonance disorders through direct visualization.

  • The mechanisms of velum and larynx are not visible on oral exams but can be observed through endoscopy, radiography or fluoroscopy.
  • Our ears may detect gross disturbance but cannot reliably discern subtleties of speech disorders. Instrumentation is able to define the subtleties of speech.
  • Instrumentation yields quantifiable, reproducible results.

How does computerized instrumentation assist the evaluation?

Special instrumentation makes diagnosis and treatment more accurate and more efficient:

  • Assessment with computerized instruments is objective and more accurate than perceptual judgments alone. Speech performance can be compared to standardized peer/group norms.
  • Pre and post measures make outcomes easier to evaluate.
  • Computers can measure several speech qualities simultaneously, e.g., pressure flow, voice and resonance measures can be measured together.
  • Objective measures can be taken during diagnostic/trial therapy to assess the effectiveness of a therapeutic technique.

What instruments are used to image the vocal tract?

  • Flexible nasal endoscopy
  • Videofluoroscopy
  • Lateral Cephalometric radiography

How does imaging assist the evaluation?

  • Allows us to view the structures and functions of the speech mechanism that are not visible during oral exam.
  • Natural speech can be observed.
  • Response to speech therapy can be observed.
  • Information from lateral fluoroscopy/radiography and endoscopy has improved the outcome of surgery for hypernasality.