Atypical pituitary abscess lacking rim enhancement and diffusion restriction with an unusual organism, Moraxella catarrhalis: A case report and review of the literature.

BACKGROUND: Pituitary abscess (PA) can be fatal if diagnosed late. Rim enhancement is a typical radiological finding of PA on postgadolinium T1-weighted magnetic resonance imaging (MRI). Diffusion-weighted imaging is helpful in distinguishing PA from other sellar cystic lesions. Herein, we report the first atypical case of PA showing neither rim enhancement nor diffusion restriction with an unusual organism, Moraxella catarrhalis. CASE DESCRIPTION: A 77-year-old woman presented with headache, polyuria, polydipsia, and fatigue for a month before presenting to a local hospital. MRI showed pituitary enlargement with contrast enhancement. She had neither fever nor visual deficits and was followed up with hormonal replacement. Six months later, she complained of visual impairment, and MRI showed further pituitary enlargement with a thickened stalk compressing the optic chiasma. Neither rim enhancement nor diffusion restriction was observed. Endoscopic endonasal transsphenoidal surgery was performed based on the radiological diagnosis of lymphocytic hypophysitis or pituitary tumors. A thick, creamy yellow pus was drained from the sellar lesion. Intraoperative rapid histopathological findings revealed polymorphonuclear leukocytes infiltrating the pituitary gland. PA was diagnosed, and irrigation and open drainage of the abscess was performed. Bacterial culture of the pus detected M. catarrhalis by mass spectrometer, confirming the diagnosis. She underwent appropriate antibiotic administration, and her visual deficits improved.
CONCLUSION: We report the first atypical case of PA showing neither rim enhancement nor diffusion restriction with M. catarrhalis. Even if preoperative findings are not suggestive of PA, it should be considered as a differential diagnosis. Intraoperative rapid histopathological findings are useful for accurately diagnosing PA and initiating appropriate surgical treatment. Copyright:

INTRODUCTION

Pituitary abscess (PA) was first described by Simmonds in 1914.[17] Although rare and occurring in 0.2–1.1% of all operated pituitary regions,[22] PA is potentially life threatening and associated with high mortality if prompt diagnosis and treatment are not instituted.[10,16] Thus, early diagnosis, prompt surgical drainage by the transsphenoidal approach, appropriate antibiotic therapy, and hormone replacement are indispensable to the treatment of PA.[26] As seen in cerebral abscess, rim enhancement on postgadolinium T1-weighted magnetic resonance imaging (MRI) is a typical radiological finding of PA,[5,15,24] though other sellar cystic lesions such as pituitary adenoma with cystic degeneration, Rathke’s cleft cyst, and cystic craniopharyngioma, which can show similar radiological appearances of rim enhancement, make the diagnosis rather difficult.[26] Diffusion-weighted imaging (DWI) has been widely used to distinguish brain abscesses from other ring-enhancing mass lesions such as certain malignancies and necrotic disease.[25] Thus, evaluation with both gadolinium-enhanced T1-weighted imaging and DWI is useful to distinguish PA from other sellar cystic lesions.[1,9,12,16,18-21] Herein, we report an atypical case of PA, suffered from Moraxella catarrhalis, showing neither rim enhancement nor diffusion restriction. In general, M. catarrhalis causes otitis media and sinusitis in children, and bronchitis and pneumonia in the elderly. To the best of our knowledge, there have been no cases of PA suffered from M. catarrhalis.

CASE REPORT

A 77-year-old woman presented to a local hospital with headache, polyuria, polydipsia, and fatigue for a month, but had no fever. Her laboratory studies showed panhypopituitarism without inflammatory findings such as an increase in white blood cells or C-reactive protein. MRI showed a 15 mm enlarged pituitary gland with heterogeneous contrast enhancement. She was referred to our hospital, where an ophthalmological evaluation showed normal visual acuity and no visual field disturbance. She was started on hormonal replacement therapy and was followed up.

Six months later, she had blurred vision in the left eye, and an ophthalmological evaluation showed a decrease in visual acuity with bitemporal hemianopia. MRI showed further pituitary enlargement with thickening of the pituitary stalk compressing the optic chiasma and a positive dural tail sign. Neither ring enhancement nor diffusion restriction was observed [Figure 1a-c]. The lesion was assumed to be lymphocytic hypophysitis or a pituitary tumor; but a histological diagnosis was needed for undertaking appropriate treatment.

Figure 1:

Brain magnetic resonance imaging scans. (a) Coronal postgadolinium T1-weighted image, (b) sagittal postgadolinium T1-weighted image, (c) axial diffusion-weighted image, and (c’) the enlarged pituitary part of diffusion-weighted image of c. (a-c’) Magnetic resonance imaging showing pituitary enlargement with heterogeneous enhancement and thickened pituitary stalk compressing the optic chiasma. There is no high signal on diffusion-weighted imaging, indicating lack of diffusion restriction. (d) Yellow and creamy pus observed intraoperatively (arrow).

Endoscopic endonasal transsphenoidal surgery was performed, and a thick, creamy yellow pus was drained out of the sellar lesion [Figure 1d]. The intraoperative rapid pathological findings showed polymorphonuclear leukocytes infiltrating the pituitary gland and no tumor cells, also reaffirmed by postoperative pathological results [Figure 2a and b]. We made an intraoperative diagnosis of PA and subsequently performed irrigation and drainage of the abscess. Postoperative MRI revealed no apparent change from preoperative MRI [Figure 3a-c]. We identified M. catarrhalis as organism by mass spectrometer (VITEK® MS). She was switched from broad-spectrum antibiotics to appropriate antibiotics; her visual function gradually recovered, while the improvement of pituitary function was not observed, and she was discharged. Written and informed consent was obtained from the patient for the publication of this manuscript and its accompanying images.

Figure 2:

The pathological result shows a predominance of polymorphonuclear leukocytes, but no tumor cells. (a) 200× and (b) 400×.

Figure 3:

Brain magnetic resonance imaging scans. (a) Coronal postgadolinium T1-weighted image, (b) sagittal postgadolinium T1-weighted image, (c) sagittal diffusion-weighted image. (a-c) Postoperative magnetic resonance imaging showing no apparent change from preoperative magnetic resonance imaging (MRI) scan. There is no high signal on diffusion-weighted imaging as same as preoperative MRI scan.

DISCUSSION

PA can be a life-threatening condition and is associated with high mortality rates.[10,13] Therefore, prompt diagnosis and treatment are crucial. However, the diagnosis of PA remains difficult because of its rarity, lack of specificity in its clinical manifestations,[2,7,22] and confounding by other, more frequent sellar cystic lesions showing similar radiological appearances of rim enhancement, such as pituitary adenoma with cystic degeneration, Rathke’s cleft cyst, and cystic craniopharyngioma.[26] It can be difficult to distinguish a brain abscess from a cystic or necrotic brain tumor on conventional MRI images. Several practical methods have been reported in conventional MRI, such as focusing on the significantly lower signal of the abscess capsule in T2WI,[8,27] and that the capsule on the ventricular side of the abscess is less well developed than the capsule on the cortical side of the abscess.[6] However, these characteristics are not always present in all abscesses. Furthermore, hypointense rims may also appear in cases of brain tumors such as metastases.[8]

DWI is useful for the differential diagnosis of PA, other sellar cystic lesions,[1,9,12,16,18-21] as well as cerebral abscesses.[25] So far, the evaluation of PA on DWI has been reported in 12 cases, summarized in [Table 1].[1,9,12,16,18-21] The finding of diffusion restriction is not always observed; Huang et al. reported that three of five patients with PA lacked this finding.[9] In contrast, all of the above-mentioned 12 cases manifested with rim enhancement. Nonetheless, neither rim enhancement nor diffusion restriction was observed in the present case, which, to the best of our knowledge, is the first such case to be reported. These findings were probably not picked up by imaging because it captures the late stages of the PA once it liquefies, as discussed by Wang et al.[24] Therefore, our case may have been in the early stages of the abscess before liquefaction.

Table 1:

Summary of rim enhancement and diffusion restriction in reports of PAs.

The development of PA is thought to be due to hematogenous dissemination[3] or by the direct extension of an adjacent infection such as sphenoid sinusitis,[4] meningitis,[22] and cavernous sinus thrombosis.[3]

Intracranial infections caused by Moraxella are very rare, and there have been few reports of intracerebral abscesses caused by M. catarrhalis.[14,23] M. catarrhalis commonly causes otitis media and sinusitis in children and bronchitis and pneumonia in the elderly with chronic obstructive pulmonary disease.[11]

To the best of our knowledge, this is the first case of PA affected by M. catarrhalis. In our case, the atypical MRI findings of PA, in addition to the abscess stage, may be related to this rare organism.

CONCLUSION

PA is rare and potentially life threatening if not promptly treated. However, its correct diagnosis is challenging. Our case reveals that PA can present without rim enhancement and diffusion restriction and M. catarrhalis can be an organism of PA. Therefore, even if PA is not suggested preoperatively, it is necessary to consider it as a possible diagnosis. Finally, intraoperative rapid histopathological findings are useful for determining the correct diagnosis of PA and instituting appropriate surgical treatment.