A 7 year-old male is referred to the Emergency 
Department (ED) with fever and neck stiffness.  Four 
days prior to this ED referral, he had come home from 
school complaining of a bad headache, nausea, sore 
throat and "neck pain."  He denied any history of neck 
or oropharyngeal trauma.  He was seen by his 
pediatrician and was noted to have a temperature of 
40.1 C.  He was diagnosed as probably having the "flu," 
and was told to drink a lot of fluids and to take 
acetaminophen for his fever.  He was again seen by his 
pediatrician today because of persistent fever, neck 
pain and he was also now complaining of a stiff neck.  
He was thus referred to the ED as a rule-out meningitis 
case.
     Upon presentation to the ED he is slightly 
tired-appearing, but non-toxic.  His vital signs are within 
normal limits with the exception of a temperature of 
39.0 C.  His airway is patent without any stridor, 
dysphagia or drooling.  His tonsils are 2+ enlarged 
bilaterally with mild erythema but no exudates.  The 
uvula is midline and there is no obvious "muffled" 
quality to this voice.  There is no obvious "bulging" of 
his retropharynx and he does not exhibit any trismus.  
He has a few 1 cm, tender cervical nodes bilaterally and 
both the Brudzinski's and Kernig's signs are negative.  
Although he does not complain of any neck pain with 
active neck flexion, he does complain of posterior neck 
pain upon active neck extension.  Palpation over the 
posterior aspect of his neck fails to reveal any areas of 
point tenderness.  The remainder of his physical 
examination is within normal limits.  

     A lumbar puncture is performed which reveals 1 
WBC and 1 RBC with normal protein and glucose 
values and no organisms seen on the gram stain.  On 
repeat examination, he still seems to complain of 
posterior neck pain with active neck extension.  A 
lateral neck radiograph is then obtained.

View lateral neck radiograph.


     Based on your interpretation of this lateral neck 
radiograph, what is your tentative diagnosis and what 
would you do to further evaluate and manage this 
disease entity?



Radiologic Discussion:
     The prevertebral space and the retropharyngeal 
space are two distinct spaces.   The retropharyngeal 
space extends from the base of the skull down to the 
level of the carina, and is located between the 
buccopharyngeal mucosa and the prevertebral fascia.  
The prevertebral space is a potential space that is 
located between the anterior aspect of the vertebral 
body and the prevertebral fascia. 

     When one suspects the possibility of a 
retropharyngeal infection (i.e., cellulitis vs. abscess), a 
lateral neck radiograph should be obtained to evaluate 
the prevertebral soft tissue thickness and contour.  The 
optimal technique to accurately assess the prevertebral 
soft tissues is to have the patient's neck in the extended 
position and to obtain the radiograph during 
end-INSPiration.  If the patient's neck is flexed and/or if 
the radiograph is obtained during end-EXPiration the 
prevertebral soft tissues may appear falsely widened 
and thus give the false impression of a possible 
retropharyngeal infection (RPI).

View a false positive radiograph.

     In the image on the left, the prevertebral soft tissues 
appear to be widened on this initial view.  However this 
view was obtained with the neck in a neutral position 
and during end-EXPiration.  The image on the right is 
the same patient, obtained with the neck extended 
(lordotic) during end-INSPiration, which demonstrates 
that the prevertebral soft tissues are actually normal.

     Note that the previously widened prevertebral soft 
tissues have now resolved with proper positioning.
 
View another example of positioning.

     This pair of lateral neck radiographs shows 
prevertebral soft tissue widening on the left image.  The 
image on the right shows the same patient with 
extension of the neck and persistence of the 
prevertebral soft tissue widening.  In this case, the 
prevertebral soft tissue widening is true. 
     Other causes of widening of the prevertebral soft 
tissue space include a mass (neoplastic or other 
causes) or hemorrhage from an occult cervical spine 
fracture.
     When attempting to evaluate the thickness of the 
prevertebral soft tissues on the lateral neck view, there 
are several methods and factors to keep in mind:

     a)  The normal thickness of the prevertebral soft 
tissues on the lateral neck view is usually < 7 mm 
anterior to C2 and < 5 mm anterior to C3/C4 (or less 
than half the diameter of the vertebral bodies).
     Although these absolute measurements can be 
utilized to assess the thickness of the prevertebral soft 
tissues, there are several other factors that should also 
be considered when evaluating the lateral neck 
radiograph.  The absolute measurement/thickness of 
the prevertebral soft tissues is not the only criteria to 
use when attempting to determine if a retropharyngeal 
infection is present.
     b)  On the lateral neck radiograph, there normally is 
a "step-off" between the posterior wall of the pharynx 
and the posterior wall of the trachea at the level of the 
larynx (approximately at the level of C4).

View "step-off".

     The vertical black lines demonstrate the "step-off" in 
this patient with croup (subglottic narrowing) and a 
normal prevertebral soft tissue region.  The upper mark 
is in line with the posterior wall of the pharynx while the 
lower mark is in line with the posterior wall of the 
trachea.  The superior-most aspect of the esophagus 
normally begins approximately at the level of C4, and 
thus normally, the posterior wall of the trachea at this 
level should NOT be in alignment with the posterior 
pharyngeal wall.  When this normal step-off is ABSENT, 
one should suspect a possible retropharyngeal 
inflammatory process (above the level of C4) which is 
causing the posterior pharyngeal wall to be displaced 
anteriorly to now be in alignment with the posterior wall 
of the tracheal air shadow.  Note that this "step-off" is 
blunted or absent in the patient with a retropharyngeal 
infection.  Examine the earlier radiographs again.


     c)  Normally the air-soft tissue interface between the 
prevertebral soft tissue and the air in the posterior 
pharynx should be very sharp.  Any inflammatory 
process of the retropharyngeal space creates an 
"indistinctness" and irregularity of this air-soft tissue 
interface.
     d)  The contour of the prevertebral soft tissue should 
normally follow the contour of the anterior aspect of the 
cervical vertebrae.

     Based on the above discussion, how would you 
interpret the lateral neck radiograph of the patient 
discussed above?

View lateral neck.


     Radiologist's interpretation:  The lateral neck 
radiograph reveals a moderate degree of soft tissue 
swelling of the prevertebral/retropharyngeal soft tissues.

     When the lateral neck radiograph suggests a 
retropharyngeal infection, a CT scan of the neck should 
be obtained to:
     a)  Delineate the extent of the infection (i.e., how far 
down the pharynx, neck and chest does the infectious 
process extend?).
     b)  Attempt to differentiate between a 
retropharyngeal cellulitis/phlegmon versus a 
retropharyngeal abscess.

       Two characteristic findings that are suggestive of 
an abscess are:
     a)  A rim of enhancement around a hypodense mass.
     b)  A convex appearance ("bulging-appearance") of 
the surface of the hypodense mass.  In contrast to this, 
a phlegmon (pyogenic cellulitis) typically does not have 
a rim of enhancement around the hypodense mass and 
the surfaces of the phlegmon do not typically exhibit a 
convex appearance. 

     A neck CT scan (with IV contrast) is obtained on the 
patient discussed above.  Based on the above 
discussion, how would you interpret this patient's neck 
CT scan?

View CT.

     Radiologist's interpretation:  There is a slight degree 
of thickening of the prevertebral/retropharyngeal 
soft-tissues.  There is a plaque-like area of hypodensity 
(arrow) anterior to the vertebral bodies and the longus 
colli muscles which probably represents a fluid 
collection in the retropharyngeal soft tissues without 
definite abscess formation.
     This case is most consistent with a retropharyngeal 
phlegmon (pyogenic cellulitis) rather than a true 
absence.  There is no rim of enhancement (with 
contrast) around the lesion and the soft tissues do not 
bulge anteriorly in a convex fashion.

View abscess example. 

     This CT scan (with contrast) shows CT findings 
more consistent with an abscess rather than a 
phlegmon.  Note the larger size, the rim of contrast 
enhancement around the lesion and the anterior bulging 
(convexity) of the prevertebral soft tissues.  These 
findings are suggestive of an abscess.

Discussion:
     Retropharyngeal abscesses are the second most 
common of the deep neck infections in children (second 
only to peritonsillar abscesses which account for up to 
50% of the deep neck infections in the pediatric 
population).
     The most common pathophysiologic etiology of a 
retropharyngeal abscess is via suppurative adenitis of 
the paramedian chains of lymphoid tissue (that drain 
the nasopharynx, adenoids and posterior paranasal 
sinuses) located in the retropharyngeal space.  Thus, 
otitis media and nasopharyngeal infections may lead to 
suppuration of these paramedian chains of lymphoid 
tissue and result in a retropharyngeal abscess.  
Because this paramedian lymph tissue usually begins 
to atrophy during the third to fourth year of life, it is no 
surprise that the majority of retropharyngeal abscess 
cases (50%) occur in children 6-12 months of age, with 
96% of the cases occurring in children < 6 years of age.
     Two other pathophysiologic etiologies of 
retropharyngeal abscesses are via:  1)  Direct 
penetrating trauma to the retropharyngeal space (i.e.,  a 
child who falls with a popsicle stick in his mouth and 
sustains direct penetration of the posterior pharynx), 
and 2)  Anterior extension of a vertebral osteomyelitis 
into the pre-vertebral soft tissue space.

     A child with a retropharyngeal infection may present 
with fever, sore throat, dysphagia and/or neck pain.  If 
the retropharyngeal infection is significant enough to 
begin to compromise the patency of the child's posterior 
pharynx, the patient may also present in a toxic fashion 
with drooling and stridor (and thus mimicking the 
presentation of a child with epiglottitis or croup).  A child 
with a retropharyngeal abscess may also present with 
meningeal signs such as neck pain/stiffness secondary 
to irritation of the paravertebral ligaments.  Although 
many textbooks comment on the fact that the posterior 
pharynx of a child with a retropharyngeal abscess may 
appear to be "bulging", in my personal experience this 
physical examination finding has not been very obvious 
in children with very early retropharyngeal infections 
(i.e., cellulitis / phlegmon).  Anterior deviation of the 
uvula may also be present in a child with a 
retropharyngeal infection.  Examination of the 
oropharynx should also be deferred if the child with a 
possible retropharyngeal abscess presents in a 
dramatic fashion with drooling and stridor.

Complications of a retropharyngeal abscess include:
     1)  Acute airway obstruction via obstruction of the 
posterior pharynx.
     2)  Aspiration secondary to the child's inability to 
handle his/her own oral secretions.
     3)  Rupture of the abscess into the pharynx resulting 
in aspiration.
     4)  Extension of the abscess causing mediastinitis, 
pneumonia or necrotizing fasciitis.
     5)  Sepsis
     6)  Dehydration secondary to the child's inability to 
tolerate oral fluids. 

     The two most common organisms recovered from 
retropharyngeal abscess cultures are Staphylococcus 
aureus and Group A beta-hemolytic Streptococcus.  A 
child with a retropharyngeal cellulitis should be 
hospitalized for intravenous antibiotics and observation 
for potential airway compromise.  If a retropharyngeal 
abscess is diagnosed on the neck CT scan, the child 
will also require surgical drainage of the abscess in 
addition to intravenous antibiotics.  Empiric antibiotic 
regimens for a child with a retropharyngeal abscess 
should cover for Staphylococcus aureus, Group A 
beta-hemolytic Streptococcus and anaerobes (i.e., 
Bacteroides).  Options include:  oxacillin, first 
generation cephalosporins, and/or clindamycin.  
Consider the empiric use of vancomycin to cover the 
possibility of methicillin resistant Staph aureus (MRSA).  
Should this possibility materialize, sepsis may result 
without adequate coverage.

Post-discussion quiz questions:

1)  The majority of retropharyngeal abscess cases 
occur in which age group?
       a)  < 1 year of age
       b)  2 - 6 years of age
       c)  7 - 10 years of age
       d)  > 12 years of age

2)  List the three pathophysiologic mechanisms which 
are responsible for producing a retropharyngeal 
abscess:
       a)
       b)
       c)

3)  What are the two most common organisms that are 
recovered from retropharyngeal abscess cultures?
       a)
       b) 

4)  The radiographic technique to optimally visualize the 
prevertebral soft tissues on the lateral neck view is 
during:
       a)  End-INSPiration with the patient's neck in the 
flexed position.
       b)  End-EXPiration with the patient's neck in the 
flexed position.
       c)  End-INSPiration with the patient's neck in the 
extended position.
       d)  End-EXPiration with the patient's neck in the 
flexed position.

5)  List at least 3 potential complications of a 
retropharyngeal abscess:
       a)
       b)
       c)


References:
     Abrunzo TJ, Santamaria JP.  Peritonsillar Abscess 
and Retropharyngeal Abscess.  In:  Strange GR, et al.  
Pediatric Emergency Medicine:  A Comprehensive 
Study Guide.  New York, McGraw-Hill;  pp.  414-416, 
1996.
     Harris JH, et al.  Radiographic Anatomy of the Neck.  
In:  The Radiology of Emergency Medicine (Third 
Edition).  Baltimore, Williams & Wilkins;  pp.  133-138, 
1993.
     Sanatamaria JP, Abrunzo TJ.  Peritonsillar Abscess 
and Retropharyngeal Abscess.  In:  Barkin RA, et al.  
Pediatric Emergency Medicine:  Concepts and Clinical 
Practice.  St Louis, Mosby Year Book;  pp.  679-681, 
1992.
     Swischuk LE.  Retropharyngeal Abscess.  In:  
Emergency Imaging of the Acutely Ill or Injured Child 
(Third Edition).  Baltimore, Williams & Wilkins;  pp.  
171-175, 1994.