A 25-year old female presented to the Emergency Department with 2 days of rigors, nuchal rigidity and intermittent confusion on a background of 3 months of left sided headaches. Her past medical history included an ovarian cyst. She was not on any regular medications apart from paracetamol. A non-contrast Magnetic Resonance Imaging (MRI) of her brain performed four weeks prior demonstrated a 19 x 11 x 13mm pituitary cystic mass described as a pituitary adenoma.

On examination, she was febrile at 38.6°C, with nuchal rigidity. She was intermittently confused, scoring 3 out of 5 on serial 7s. She had no other neurological deficits. Her visual acuity was 6/5 bilaterally. Her visual fields were normal on confrontation testing and she had full range of eye movements. There was no papilloedema. A Gadolinium-enhanced MRI of her brain revealed a rim enhancing pituitary cystic lesion measuring 12.8 x 21 x 14mm that had increased in size and was impinging on the optic chiasm (Figure 1).

Figure 1: A  Gadolinium enhanced MRI brain reveals a rim enhancing pituitary lesion measuring 12.8 x 21 x 14mm.

A lumbar puncture showed 1777x 10⁶ leucocytes, 70% polymorphonuclear cells, 30% mononuclear cells, an elevated protein of 0.83 g/L (0.15-0.45) and a low glucose of 2.3 mmol/L (2.8-4.2). There were no organisms on gram stain. The cerebrospinal fluid was negative for Streptoccocus pneumoniae, Neisseria meningitidis and acid-fast bacilli. She had a peripheral leucocytosis with a white cell count of 18.x 10⁹/L (4.0-12.0). Her HIV serology was non-reactive.

Given the ongoing fevers and meningism, there was a high index of suspicion for an infective process. She was commenced on intravenous benzylpenicillin, aciclovir, ceftriaxone and metronidazole. She received a single dose of dexamethasone and then was commenced on regular intravenous hydrocortisone pre-operatively. Her initial pituitary panel (after dexamethasone) revealed a low TSH and T4, appropriately suppressed ACTH and cortisol but no other abnormalities (Table 1).

The patient had a transsphenoidal pituitary fossa exploration and frank pus was drained from the sella. Sixteen hours post-operatively, she developed polyuria and was treated with 1mg of intravenous desmopressin.  Due to ongoing polyuria, she was converted to a regular intranasal dose of 10mcg twice daily.  Her intravenous hydrocortisone was weaned to oral cortisone acetate and she was commenced on levothyroxine 75mcg.

Histological examination of the lesion revealed minimally inflamed pituitary gland tissue, fragmented proteinaceous debris with small numbers or neutrophils and focal benign epithelial lining suggestive of a Rathke’s cleft cyst with superimposed inflammation. No pathogen was isolated from the pituitary abscess. She recovered rapidly and was discharged 5 days after her operation and continued intravenous ceftriaxone, oral metronidazole and oral doxycycline in the community for 4 weeks.

Eight weeks following her operation, a repeat pituitary panel did not demonstrate any abnormalities (Table 1).

Her thyroxine and cortisone were reduced to 50 mcg and 12.5mg BD respectively. She continued intranasal desmopressin.  By this time, her menses had recommenced and headache had resolved.

In summary, a 25-year old immunocompetent female presented with crescendo headaches and was found to have an infected . No pathogen was found but she was managed empirically with antibiotics prior to surgery.  At last follow up, she demonstrated partial recovery of her pituitary function.

Case discussion

We describe a case of a secondary pituitary abscess from an infected Rathke’s cleft cyst in a patient with no identifiable risk factors who required thyroxine, cortisone and desmopressin post-operatively.

Pituitary abscesses are rare but serious intrasellar infections reported to comprise less than 1% of all cases of pituitary disease referrals in a tertiary specialist centre [1]. Most pituitary abscess occur in a previously healthy gland, while secondary pituitary abscess represent one-third of all pituitary abscesses[2]. The two common routes of abscess formation are haematogenous seeding, or direct extension from infected adjacent structures (eg meningitis, thrombophlebitis or sphenoid sinusitis). Common clinical manifestations include headache, visual disturbance, and features of pituitary insufficiency. The diagnosis of a pituitary abscess  may be delayed due to the lack of systemic signs of inflammation (occurring only one-third of patients[3]), especially that radiologically, they are often mistaken for pituitary adenomas [4].

Rathke’s cleft cyst (RCC) is an epithelial cell-lined cystic pituitary lesion derived from the remnant of Rathke’s pouch which is usually asymptomatic. To date, there have been 21 cases of pituitary abscess from Rathke’s cleft cyst published. Nine patients had endocrine dysfunction; 3 had multi-axis anterior failure, 3 had diabetes insipidus (DI) and 3 had hyperprolactinaemia at initial presentation. The latter 2 were caused by a stalk effect. In one patient, the was not specified. All but 1 patient presented with headache and/or visual disturbance; clinical signs of meningism were found in only 5 of 21 patients.

Most patients with RCC abscess presented after several months of symptoms. Rim-enhancement is a common feature on MRI. However, as the signal intensity of an abscess may be affected by its protein content, its appearance may be variable on MRI [5].

Once diagnosis is made, surgery should be performed promptly via a transsphenoidal approach as this provides a route for prolonged drainage and decompression of the suprasellar structures. Craniotomy is not routinely recommended due to the higher risk of exposure of infectious material to adjacent structures. Of the published 21 cases with an infected Rathke’s cleft cyst, 8 had positive cultures from the abscess content: Acinetobacter, Staphylococcus epidermis, Staphylococcus aureus, Streptococcus pyogenes and Enterococcus faecium [6]. Whilst our patient did not have a positive culture, this may be due to the use of empirical antibiotics administered pre-operatively. Another differential that cannot be excluded is chemical meningitis.

Pituitary abscess formation within RCCs do not often cause DI. Furthermore, DI in RCCs have only been described in case reports describing atypical location of the cyst at the pituitary stalk, rapid growth, primary inflammation, stalk impairment or co-existence with destructive pituitary lesion[2].  A retrospective study of 700 patients who underwent endoscopic TSS for resection of a pituitary adenoma, RCC or craniopharyngioma found an overall rate of postoperative DI of 14.7%, but only 4.6% of patients had permanent DI (defined as the need for desmopressin more than 1-year post-operatively)[7]. Patients with RCC had a higher risk of developing DI compared to those with a pituitary adenoma (OR =2.2; 95% CI 1.2-3.9; P=0.009). In patients who underwent TSS for RCC, 26% developed post-operative DI while 10.3% developed permanent DI.

In conclusion, we have described a rare case of secondary pituitary abscess complicated by DI in a young non-immunocompromised and otherwise healthy patient.

Take home points:

• Rathke’s cleft cyst abscesses are difficult to diagnose before surgery due to their indolent course of non-specific clinical symptoms and radiological findings.
• Symptoms may arise from mass effect (headache or visual disturbance) or pituitary hormone deficiency
• Whilst there are no specific features on MRI, a rim-enhancing cystic lesion should raise suspicion of the possibility of an abscess
• Surgery should occur promptly as source control of the infection alongside antibiotics