Diagnosis of PDH
A 16-year-old, castrated male English Cocker spaniel dog was presented with a 4 year history of dermatological problems such as alopecia and pruritus. Polyuria and polydipsia were not noted by the client. Physical examination revealed a distended abdomen, generalized alopecia, and seborrheic dermatitis. Increased alkaline phosphatase activity (ALP: 660 IU/L, reference range: 29–97 IU/L) was observed on the serum chemistry panel. The levels of total cholesterol (221 mg/dL, reference range: 135–270 mg/dL) and triglycerides (76 mg/dL, reference range: 21–116 mg/dL) were within the reference range. Hepatomegaly and bilateral enlarged adrenal glands of relatively equal size (left: 6.2 mm, right: 5.9 mm in thickness of the cranial poles) were identified on abdominal radiographs and ultrasonography, respectively. Because these findings suggested hyperadrenocorticism, an ACTH stimulation test and a high-dose dexamethasone suppression test (HDDST) were performed. The serum samples were obtained for the ACTH stimulation test before and 1 h after intravenous administration of 0.25 mg synthetic ACTH (Synacthen, Novartis Pharma, Basel, Switzerland); pre-ACTH cortisol concentration was 226.2 nmol/L (reference range: 14–166 nmol/L) and post-ACTH concentration was 717.3 nmol/L (reference range: 166–469 nmol/L). Serum cortisol concentration was suppressed after administration of dexamethasone (0.1 mg/kg intravenously [IV]; Je-Il Pharm, Daegu, South Korea): pre-HDDST cortisol concentration was 69.5 nmol/L and 4-h and 8-h post-HDDST cortisol concentrations were 40 nmol/L and <27.6 nmol/L, respectively. Based on these results, a diagnosis of PDH was made.
FDG-PET and 7 T MRI fusion imaging
To evaluate the pituitary gland region, intracranial imaging was performed using a high-resolution research tomography (HRRT)-PET and 7 T MRI fusion imaging system, with the owner’s permission. Written client consent was obtained prior to examination, and this procedure was performed with the approval of our institutional review board committee. The dog was fasted for 12 h, and then injected with FDG (0.4 mCi/kg IV); the dog was kept caged for 1 h to minimize movement and ensure a stable FDG uptake. The FDG-PET scan was conducted for 30 min on the HRRT device (resolution, 2.5 mm full width at half maximum resolution in three-dimensional [3D] acquisition mode; ECAT HRRT; Siemens, Knoxville, TN, USA) under general anesthesia maintained by tiletamine/zolazepam (8 mg/kg IV; Zoletil; Virbac, Carros, France) following medetomidine (20 μg/kg intramuscularly [IM]; Domitor; Pfizer, Seoul, South Korea) premedication. Immediately after the PET scan, the shuttle system transported the dog to 7 T-MRI scanner (Magnetom 7 T; Siemens, Berlin, Germany), and then pre- and post-contrast T1-weighted 3D magnetization-prepared rapid gradient echo images (TR: 3000 ms, TE: 2.98 ms, TI: 1100 ms, flip angle: 10°, matrix: 192 × 256 × 256, field of view [FOV]: 96 × 128 mm2, slab thickness: 128 mm) and transverse T2-weighted turbo spin echo images (TR: 3000 ms, TE: 72 ms, flip angle: 60°, matrix: 384 × 384, FOV: 100 mm, slice thickness: 1.5 mm, interslice gap: 0 mm) of the brain were obtained. To minimize personnel radiation exposure, the dog was remotely monitored in the approved holding facility during the recovery from anesthesia.
On MRI, an arcuate lesion was noted in the right-ventral part of the pituitary gland. It had hypointensity on pre-contrast T1-weighted images (WI) (Figs. 1a and 2a) and hyperintensity on T2-WI (Fig. 2c). This adenohypophyseal lesion displaced the neurohypophysis in the left-dorsal direction. Pre-contrast T1- and T2-WI of the neurohypophysis showed hyperintensity (Figs. 1a and 2a) and isointensity (Fig. 2c), respectively. Following administration of gadolinium-diethylenetriamine pentaacetic acid (0.1 mmol/kg IV; Omniscan; Nycomed, Princeton, NJ, USA), signal intensity was increased uniformly in the neurohypophysis, while the adenohypophyseal lesion had no enhancement (Fig. 2b). The height of the pituitary gland was 4.16 mm and pituitary height/brain area (P/B) ratio was 0.3. These MRI findings were consistent with pituitary microtumor. The FDG uptake of the pituitary gland was not elevated on HRRT-PET scan (Fig. 1b and c). The standardized uptake value (SUV) was lower in the pituitary gland (SUV: 1.23) than in the gray matter (SUV: 3.95). The anatomical location of the pituitary gland was more precisely identified by the PET-MRI fusion images (Fig. 1c).
Follow-up MR scan
The dog was treated with trilostane (3 mg/kg orally [PO], twice daily [BID]; Vetoryl; Dechra, Shrewsbury, UK), and then post-ACTH cortisol concentration had been maintained between 2 and 5 μg/dL. Six months after initial MRI, a pituitary lesion was monitored by 3 T MRI scan (Achieva 3.0 T multi TX; Philips Healthcare, Best, NL) with following sequences: pre- and post-contrast T1-weighted spin echo imaging (TR: 500 ms, TE: 12 ms, flip angle: 90°, matrix: 256 × 256, FOV: 150 mm, slice thickness: 3 mm, interslice gap: 0 mm) and T2-weighted turbo spin echo imaging (TR: 4000 ms, TE: 80 ms, flip angle: 90°, matrix: 304 × 294, FOV: 130 mm, slice thickness: 3 mm, interslice gap: 0 mm). Although the height (4.67 mm) and P/B ratio (0.31) of the pituitary gland were slightly increased, other MRI findings were not different from the first MRI scan (Fig. 2d–f). Presently, the dog is managed well without dermatological or neurological abnormalities.
