A cervical tuberculous abscess mimicking a fourth branchial cleft cyst in a child: PCR, the key to fast diagnosis

Anterior cervical tuberculous abscess is a rare presentation of extrapulmonary tuberculosis even in endemic countries. We report a case of a 14-year-old girl with a 5 day history of an anterior mass. The diagnosis of an infected fourth branchial cleft cyst was first evoked. Fine-needle aspiration cytology was suggestive of tuberculosis. Polymerase chain reaction analysis was the key to the diagnosis of a tuberculous abscess. In endemic countries, abscesses occurring in uncommon sites should be dealt with a high degree of suspicion for tuberculosis. Early diagnosis is essential to initiate specific and effective treatment. Pre-operative diagnosis avoids invasive surgery and related complications.


Background
The incidence of extrapulmonary tuberculosis (EPT) is on the rise in developing but also in industrialized countries. Cervical lymph nodes are the most commonly affected site [1]. EPT may have different clinical presentations making diagnosis difficult. Cervical tubercular abscess is a rare presentation of extrapulmonary tuberculosis. Its clinical presentation may be atypical requiring various investigations to make the diagnosis. Non-invasive fast diagnostic tools are helpful to reduce time to diagnosis with the probability of tuberculosis always in mind in endemic countries.

Case presentation
A 14-year-old girl presented with a 5-day history of an enlarging anterior mass of the neck. She had no difficulty in swallowing or breathing and no loss of appetite or weight.
She had no general symptoms such as asthenia, sweats, or fever. No social promiscuity or immune deficiency was identified. She also denied sore throat, cough, or sputum production. Her vaccination was complete for her age. Physical examination revealed a 4-cm firm mass in the right anterolateral part of lower neck. There were no inflammatory signs or tenderness. The mass was not mobile on protrusion of the tongue or swallowing. There was no cervical lymphadenopathy.
The biological assessment showed normal cell count and no signs of infection; TSH was 2.53 IU/ml and FT4 1.11 ng/dl. Tuberculosis skin test was negative. Ultrasonography showed a heterogeneous lesion over the right paramedian region of the neck, lateral to the thyroid lobe. Cervical CT scan showed a hypodense lesion with fluid attenuation and enhanced rim of the right paramedian space, lateral to the trachea and the thyroid lobe, extending to the ipsilateral paralaryngeal space with a mass effect on the esophagus (Fig. 1).
The diagnosis of infected cyst of the fourth branchial cleft was first evoked, but the atypical presentation and the negative infectious biological balance incited to further investigations.
The fine-needle aspiration cytology (FNAC) of the swelling revealed the presence of Langerhans giant cells along with an epithelioïd granuloma that was suggestive of tuberculosis. A quick additional argument in favor of the diagnosis was needed to confirm the diagnosis justifying a long and potentially aggressive medical treatment and avoid an invasive surgery.
The PCR GeneXpert®, performed on the puncture fluid, detected Mycobacterium tuberculosis complex and no rifampicin resistance.
As a result, surgical drainage of the abscess was no longer indicated, and the patient was started on antituberculous therapy. Microbiological culture was positive for Mycobacterium tuberculosis complex, and the diagnosis of tuberculous abscess was confirmed.
The patient received weight-adjusted doses of isoniazid (H), rifampicin (R), pyrazinamide (Z), and ethambutol (E) for 2 months, followed by H and R for a duration of 6 months. The swelling totally disappeared at the end of the second month of treatment.
Patient did not present any complications of antituberculous drugs. There was no recurrence or reactivation of the disease at 10-months follow-up.

Discussion
Tuberculosis (TB) remains one of the biggest health problems in developing and industrialized countries [2] with extrapulmonary tuberculosis (EPT) representing an increasing proportion reaching 20 to 40% [3].
In Tunisia, the incidence of EPT is also on the rise and a growing interest in EPT is observed [3]. The most common site of extrapulmonary disease is lymph node especially the cervical group (60-90%).
The incidence of tuberculosis in children has been continuously rising around the world. EPT cases account for one third of these instances [4,5].
EPT may have different clinical presentations rendering the diagnosis difficult compared to pulmonary tuberculosis. An estimated one third of new cases remain undiagnosed every year [3]. The treating clinicians should be aware of all the rare presentations of the disease [4,6].
Anterior cervical swelling may suggest different etiologies such as branchial cysts, inflammatory and infectious lymphadenitis, and neoplastic causes [7]. The anterior lymph node group may mimic a thyroid nodule or a thyroglossal cyst [8].
When indicated, an ultrasound is the first-line radiological examination. Tuberculous node appears as a hypoechogenic lesion, with intranodal cystic calcifications and necrosis that is dense with posterior acoustic shadow. On CT scan, the lesions may appear homogeneous, entirely calcified, or have a low-attenuation central zone and an enhancing rim [9].
FNAC has a high diagnostic accuracy in detecting tuberculosis with sensitivity of 93.1% and specificity of 100%. Cytological criteria include clusters of epitheloid cells with or without necrotic debris, mature lymphocytes, and pleomorphic lymphoid cells [10].
The absence of specific clinical presentations and high morbidity rates caused by diagnostic difficulties and delays make the use of new diagnostic tools necessary. Mycobacterial culture which is the gold standard method for TB diagnosis has a long incubation period (2-8 weeks) and a low sensitivity. Faster diagnostic techniques are essential to initiate specific and effective treatment. Molecular diagnostic tools such as GeneX-pert® can detect mycobacterium complex as well as resistance to rifampicin. According to Marouane et al., the sensitivity of the GeneXpert® test was 87.5% in biopsies, 80% in pus and abscesses, and 66.7% in biological fluids [3]. This test helped us reduce time to diagnosis in front of an atypical acute presentation and avoid an invasive surgical procedure. A patient with a neck swelling not responding to antibiotics should receive a puncture with PCR study and FNAC, if tuberculosis is suspected, prior to further investigation by invasive procedures such as surgical biopsy [11].
Only a few cases of cervical tuberculous abscesses have been reported. We diagnosed this case preoperatively thanks to FNAC and PCR.

Conclusion
The occurrence of abscesses in uncommon sites should be dealt with high degree of tuberculosis suspicion in endemic countries. Pre-operative diagnosis avoids invasive surgery and related complications.