Retropharyngeal infection most commonly occurs in children aged younger than 6 years. Early detection of a developing retropharyngeal abscess can alleviate the need for surgical drainage. Infections originate in the lymphatic chains that drain the upper airway and pharynx. By 3 to 4 years of age, the retropharyngeal lymph node system begins to atrophy, and the risks of inflammation and infection subsequently decrease .
Although retropharyngeal abscesses have few specific symptoms, 50% of patients experience fever, stiff neck, neck pain, and difficulty swallowing . However, retropharyngeal abscesses often occur after upper respiratory tract infections, and these symptoms are not specific to the development of an abscess. Previous studies reported that the most common symptoms at presentation were decreased oral intake (92%), neck pain (89%), and neck swelling or mass (79–83%) . Although it is not uncommon for patients with retropharyngeal abscesses to present with a main complaint of neck swelling, this is often associated with enlarged lymph nodes or a deep neck abscess, and none of the previously reported cases had a cystic lymphangioma.
CT angiography is an effective diagnostic imaging modality for the detection of retropharyngeal abscesses . Contrast-enhanced CT is the radiological modality of choice for evaluating retropharyngeal abscesses, and is highly sensitive but not very specific. MRI is better than CT for imaging soft tissue masses such as cystic lymphangiomas. We believe that CT angiography is also useful for the investigation of retropharyngeal abscesses.
Because retropharyngeal abscesses are often accompanied by upper respiratory tract infections, the microorganisms isolated from these abscesses are often similar to those isolated from patients with upper respiratory tract infections. In a study by Hoffmann et al.,  the bacteria isolated from retropharyngeal abscesses included Streptococcus spp. (72%), S. pyogenes (41%), Staphylococcus aureus (13%), Candida (6%), and Haemophilus influenzae (3%). The proportion of cases with S. aureus infection was particularly high in children aged less than 1 year. The rates of detection of methicillin-resistant S. aureus are increasing. Many patients have also been shown to have mixed infections. Brook  performed needle aspirations on 14 paediatric patients with retropharyngeal abscesses and found that 12 had mixed anaerobic and aerobic infections, including Streptococcus spp., S. aureus, and H. influenzae. Studies by Asmar  and Craig et al. had similar findings. However, antibiotic-resistant bacteria were rarely isolated in these studies, suggesting that isolation of PRSP in the current patient can be attributed to the high prevalence of antibiotic-resistant bacteria in Japan .
Lymphangiomas are uncommon lesions of the lymphatic channels, and are often present at birth and usually diagnosed during childhood, mostly before the age of 2 years. Diagnosis is by MRI and fine-needle aspiration cytology findings . In the past, surgery was the treatment of choice for lymphangiomas. However, because of surgical complications including nerve injury, cyst recurrence, and cosmetic problems, OK-432 therapy has recently become the treatment of choice. Injection of OK-432 into the cyst produces inflammation [14, 15], and induction of cytokines in the cells of the cyst wall results in fibrotic adhesions in the cyst with resolution of fluid accumulation. In the present case, we hypothesize that inflammation arising from the retropharyngeal abscess also caused inflammation of the congenital lymphangioma. The cystic lymphangioma then remained inflamed after resolution of the retropharyngeal abscess, but resolved after OK-432 therapy.
Lymphangiomas and retropharyngeal abscesses are both known to be more common in children than in adults. However, we found no other reports of concomitant presentation of lymphangioma and retropharyngeal abscess in the literature. Concomitant occurrence of these conditions may increase with increasing age.