Clinical Report: Rare Collision Tumor of ACTH-Producing PitNET and Pituicytoma
Overview
This case study details a rare collision tumor comprising an ACTH-secreting pituitary neuroendocrine tumor (PitNET) and a pituicytoma in a 21-year-old woman presenting with Cushing’s disease. Histopathological, immunohistochemical, and ultrastructural analyses confirmed two distinct neoplasms coexisting in the sellar region, highlighting diagnostic challenges and the importance of comprehensive evaluation.
Background
Collision tumors are rare entities characterized by two distinct neoplasms coexisting in the same anatomical site without histological intermingling. Pituitary collision tumors involving PitNETs and pituicytomas are exceptionally uncommon, with limited clinicopathological characterization. Pituicytomas are benign WHO Grade I tumors arising from neurohypophyseal glial cells, while corticotroph PitNETs cause Cushing’s disease through excessive ACTH secretion. Preoperative diagnosis is difficult due to overlapping clinical and radiological features with typical PitNETs, necessitating detailed histopathological and immunohistochemical assessment.
Data Highlights
Parameter
Value
Reference Range
Fasting plasma glucose
83 mg/dL
70–110 mg/dL
Serum creatinine
0.79 mg/dL
0.46–0.90 mg/dL
Sodium
142 mEq/L
135–145 mEq/L
Potassium
4.4 mEq/L
3.5–5.0 mEq/L
Total calcium
10.3 mg/dL
9.0–10.7 mg/dL
Ionized calcium
1.16 mmol/L
1.16–1.32 mmol/L
Total cholesterol
189 mg/dL
<200 mg/dL
HDL cholesterol
64 mg/dL
>50 mg/dL
LDL cholesterol
115 mg/dL
<140 mg/dL
25-hydroxyvitamin D
27 ng/mL
>30 ng/mL
Cortisol
30.2 μg/dL
3.7–19.4 μg/dL
ACTH
89.3 pg/mL
7.3–63.3 pg/mL
Total testosterone
0.71 ng/dL
0.12–0.48 ng/dL
S-DHEA
460 μg/dL
61.2–511.7 μg/dL
Urinary free cortisol
190.9 μg/day
4.3–176 μg/day
Late-night salivary cortisol
0.75 μg/dL
<0.41 μg/dL
Post-dexamethasone cortisol
39.7 μg/dL
<1.8 μg/dL
TSH
0.07 U/mL
0.27–4.2 U/mL
Free T4
0.74 ng/dL
0.93–1.7 ng/dL
Key Findings
Identification of a 4 mm microadenoma in the left lateral recess of the sellar region on MRI, consistent with a PitNET.
Histopathology confirmed a corticotroph PitNET with diffuse ACTH immunostaining and a Ki-67 proliferation index of 4%.
Coexisting pituicytoma characterized by increased neoplastic proliferation, nuclear TTF-1 positivity, and a Ki-67 index of 3%.
Ultrastructural analysis demonstrated two morphologically distinct tumor populations without histological admixture.
Postoperative development of diabetes insipidus, with the patient achieving clinical and biochemical remission at nine months.
Rare association of pituicytoma with pituitary hyperfunction and Cushing’s disease highlighted by this case.
Clinical Implications
Clinicians should consider the possibility of collision tumors in patients presenting with pituitary lesions, especially when clinical or radiological features are atypical. Definitive diagnosis relies on thorough histopathological and immunohistochemical evaluation, as preoperative imaging may not distinguish dual pathology. Awareness of such rare entities can guide surgical planning and postoperative management, including monitoring for complications like diabetes insipidus.
Conclusion
This case underscores the exceptional rarity of collision tumors involving an ACTH-producing PitNET and a pituicytoma, emphasizing the need for detailed pathological assessment to ensure accurate diagnosis and optimal patient management. Reporting such cases enhances understanding of complex pituitary tumor biology and informs clinical practice.
References
Original Case Study, 2024 -- Uncommon Collision Tumors Involving an ACTH-Producing Pituitary Neuroendocrine Tumor and Pituicytoma
by Silvia Carolina Fernández, María Celina Bernhardt, Ezequiel Grondona, Carolina Leimgruber, Virginia Juárez, Ana Clara Venier, María Lorena Bertolino, Emilio Mezzano, Jorge Humberto Mukdsi, Favio Nicolás Pesaola, Ana Lucía De Paul
