Suboccipital extracranial and intracranial abscess of a neonate: an exceedingly rare occurrence

Background

Intracranial abscess is a rare condition affecting children. Reportedly, the subdural space is the preferred site for identifying this infection. Some risk factors have been described, such as prior sinusitis, otitis media, dermoid cyst and head trauma. Another unexpected factor associated with these infections was iatrogenic complications after development of a line vein on the scalp.1–7 Currently, the extradural space is considered the rarest region where such intracranial abscesses can occur, and the classic entity is referred to as a Pott’s puffy tumour is the most recognisable example in which the abscess simultaneously affects the extradural and extracranial spaces on the frontal region as a complication of sinusitis.3 However, this kind of abscess has not been described in the posterior fossa previously.

We report a case of a newborn with a mass in the suboccipital region caused by an extracranial and intracranial abscess that should be considered as an important differential diagnosis of a suboccipital cutaneous mass in newborns.

Case presentation

A 2-month-old boy was brought to our hospital due to a rapidly growing oedematous formation in the suboccipital region. The mother reported that the child had a 3-day fever 1 month earlier without an identifiable cause, and spontaneous remission was observed. No other symptoms and no use of antibiotics were reported. Moreover, this boy had no history of head trauma, congenital diseases, otitis or skin infections. Additionally, the mother reported an uneventful pregnancy with a delivery at full term and a weight of 3500 g.

On physical examination, the patient showed a soft mass occupying the suboccipital region without pain or skin abnormalities while maintaining normal behaviour without irritability (figure 1). In addition, no compromise of the child’s motor function or feeding capacity was noted. During observation, the mass enlarged considerably, so we performed neuroimaging.

Investigations

Head CT with three-dimensional reconstruction was performed, which showed an intracranial component in continuity with an extracranial cystic aspect. Moreover, fluid in the intracranial space was compressing the right cerebellar hemisphere, which appeared to have caused erosion of the occipital bone (figures 1 and 2). To obtain more information, MRI was performed and showed peripheral gadolinium enhancement (figure 3).

Blood sampling of the suboccipital mass with subsequent laboratory testing showed the following findings: erythrocyte sedimentation rate, 83 mm³/hour (reference=10 mm³/hour); erythrocyte count: 2.67×10⁶/mm³ (reference=3.8×10⁶/mm³); haemoglobin, 76 g/L (reference=11.5 g/dL); platelet count, 0.451/L (reference=150–400/mm³) and leucocyte count, 9.130 /mm³ (reference=5–17 000/mm³). The relative counts were as follows: neutrophils, 46.3%; lymphocytes, 42.8%; monocytes, 10%; eosinophils, 0.9% and C reactive protein, 3.9 mg/dL (reference=<1 mg/dL).

Differential diagnosis

First, considering the rapid growth of the mass without other patient symptoms, the main diagnostic hypothesis was subcutaneous infection. However, the patient had no skin inflammatory symptoms.

Second, posterior fossa lesions affecting children usually have a neoplastic nature until proven otherwise. Considering this premise, our other hypothesis was a neoplastic disease, such as haemangiopericytoma and pilocytic astrocytoma. However, the extracranial component led us to suppose unusual bone tumours, such as osteosarcoma, or tumours that arise from muscles, such as rhabdomyosarcoma.

Finally, the infection hypothesis was considered because of the rapid growth of the lesion and its unusual behaviour, which compressed the surface of the dura and cerebellum and led to erosion of the occipital bone.

Treatment

The open surgical approach was chosen, and under general anaesthesia, the boy was placed on the ventral decubitus position, and a linear incision was made above the mass. A massive collection of pus was observed after the suboccipital muscles were incised, and a syringe was used to collect an aliquot of the infectious fluid (figure 4).

After the extracranial pus was drained, a small hole on the right side of the suboccipital bone was confirmed, and the intracranial component was evacuated. Curettage was performed on the surface of the dura to remove the residual inflammatory cells, and a dural tear was avoided, which minimised dissemination of the infection to the central nervous system. A small bone sample was removed from the border of the skull hole for analysis. No drains were inserted, and non-absorbable stitches were used to close the skin.

Postoperatively, the culture stain of the pus and bone samples was positive for Staphylococcus aureus, and the patient was administered antibiotic therapy with vancomycin for 40 days without complications.

Outcome and follow-up

After discharge from the hospital, the patient achieved normal growth and development milestones without neurological alterations. No abscess recurrence was observed during the 8-year follow-up, and no cerebellar signs, such as ataxia, dysdiadochocinesia, speech alterations or dysmetria, were observed throughout the follow-up, and the boy had acceptable school performance.

Contrast-enhanced CT performed on the final follow-up showed total recovery of cerebellar morphology without parenchymal abnormalities (figure 5). Furthermore, the eroded bone was not ossified.

Thus, the cryptogenic suboccipital abscess hypothesis was confirmed.