Sheehan's syndrome pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: :Iqra Qamar M.D.[2]
Overview
- It is thought that Sheehan's syndrome is the result of ischemic necrosis of pituitary gland due to pituitary gland enlargement during parturition precipitated by hypotension due to massive hemorrhage. Apart from pituitary gland enlargement during and before parturition, vasospasm, generalized Schwartzman phenomenon, thrombosis and compression of the hypophyseal arteries, autoimmunity, DIC and smaller size of sella are thought to play a contributing role in pathogenesis of sheehan syndrome.[1][2][3] Occlusion and other vascular abnormalities of the hypophyseal portal system can also cause complications in the exchange of hormones between the hypothalamus and the pituitary gland leading to hypopituitarism.
- Sheehan's syndrome results in mild to severe pituitary dysfunction resulting in partial or panhypopituitarism such as GH, thyroid hormone, glucocorticoid, gonadotropins (LH, FSH) and prolactin hormone deficiencies that manifests as a wide spectrum of presentation.[4] Usually, GH is the earliest one to be lost.[1]
Pathophysiology
| DIC‡ | Severe PPH† | Glandular hypertrophy and hyperplasia | Small sella size | Autoimmunity | |||||||||||||||||||||||||||||||||||||||||||||
| Hypotension/Shock | Pituitary enlargement | Pituitary compression | |||||||||||||||||||||||||||||||||||||||||||||||
| Blood supply compression | |||||||||||||||||||||||||||||||||||||||||||||||||
| Ischemic necrosis | |||||||||||||||||||||||||||||||||||||||||||||||||
| Hypopituitarism | |||||||||||||||||||||||||||||||||||||||||||||||||
| Amenorrhea | Agalactorrhea | Secondary adrenal insufficiency | Hypothyroidism | ||||||||||||||||||||||||||||||||||||||||||||||
‡Disseminated intravascular coagulation (DIC) Amniotic fluid embolism or HELLP Syndrome.
†Postpartum hemorrhage (PPH) i.e. >500 ml after vaginal delivery or 1000 ml after C-section.
Pathogenesis
- Pituitary gland is amongst the most vascularized tissues in the body that normally weighs about 0.5g but gets doubled in size during pregnancy.[5]
- Pituitary gland enlargement due to hypertrophy and hyperplasia of lactotrophic cells in anterior pituitary resulting in superior hypophyseal artery compression complicated by decreased portal pressure and vasospasm during delivery, play an important role in the pathogenesis of Sheehan's syndrome.[6]
- Apart from Pituitary gland enlargement during and before parturition, vasospasm, generalized Schwartzman phenomenon , thrombosis and compression of the hypophyseal arteries, autoimmunity, DIC and smaller size of sella are understood to play a role in the pathogenesis of Sheehan syndrome.[1][3][7]
- It is believed that tissue necrosis results in release of sequestered antigens, precipitating autoimmunity of the Pituitary gland and hypopituitarism in Sheehan's syndrome.[8]
- Type 1 diabetes, pre-existing vascular diseases and any pituitary masses are associated with increased risk of developing Sheehan's syndrome in pregnancy. [9]
Anterior pituitary
- Anterior pituitary does not have a direct blood supply and is supplied by hypophyseal portal system.
- The hypophyseal portal system is a fenestrated set of capillaries and allows rapid exchange of hormones between hypothalamus and anterior pituitary.
- Occlusion and other vascular abnormalities of the hypophyseal portal system can also cause complications in the exchange of hormones between the hypothalamus and the pituitary gland leading to hypopituitarism.
Posterior pituitary
- Posterior pituitary has its own blood supply via inferior hypophyseal artery and is less commonly affected as compared to anterior pituitary.
- If posterior pituitary is affected, it can result in neurohypophseal dysfunction and ischemic necrosis of thirst center leading to increased osmotic threshold for thirst onset.[10]
- Severe PPH (loss of >500ml of blood during the first 24hr) leading to hypotension and ischemic necrosis of pituitary gland is the most common cause of Sheehan's syndrome.[1]
- Sheehan's syndrome results in mild to severe pituitary dysfunction resulting in partial or panhypopituitarism such as GH, thyroid hormone, glucocorticoid, gonadotropins (LH, FSH) and prolactin hormone deficiencies that manifest as a wide spectrum of presentation.[4]
- Usually, GH levels decrease before others.[1]
Genetics
There is no genetic association found to be associated with Sheehan's syndrome.
Associated Conditions
Sheehan's syndrome is associated with:
Gross Pathology
- On gross pathology, pituitary gland follows sequential changes of enlarged pituitary gland to a small shrunken/atrophic gland later on replaced by remnants of pituitary or CSF.
Microscopic Pathology
On microscopy, the following findings may be observed:
- Ischemic necrosis leading to scarring of neurohypophysis
- Scarring of paraventricular and supraoptic nuclei
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References
- ↑ 1.0 1.1 1.2 1.3 1.4 Keleştimur F (2003). "Sheehan's syndrome". Pituitary. 6 (4): 181–8. PMID 15237929.
- ↑ Apitz, Kurt (September 1, 1935). "A Study of the Generalized Shwartzman Phenomenon". The Journal of Immunology. 29 (3): 255–266.
- ↑ 3.0 3.1 McKay, Donald G.; Merrill, Samuel J.; Weiner, Albert E.; Hertig, Arthur T.; Reid, Duncan E. (1953). "The pathologic anatomy of eclampsia, bilateral renal cortical necrosis, pituitary necrosis, and other acute fatal complications of pregnancy, and its possible relationship to the generalized Shwartzman phenomenon". American Journal of Obstetrics and Gynecology. 66 (3): 507–539. doi:10.1016/0002-9378(53)90068-4. ISSN 0002-9378.
- ↑ 4.0 4.1 Vance ML (1994). "Hypopituitarism". N. Engl. J. Med. 330 (23): 1651–62. doi:10.1056/NEJM199406093302306. PMID 8043090.
- ↑ Rolih CA, Ober KP (1993). "Pituitary apoplexy". Endocrinol. Metab. Clin. North Am. 22 (2): 291–302. PMID 8325288.
- ↑ Scheithauer BW, Sano T, Kovacs KT, Young WF, Ryan N, Randall RV (1990). "The pituitary gland in pregnancy: a clinicopathologic and immunohistochemical study of 69 cases". Mayo Clin. Proc. 65 (4): 461–74. PMID 2159093.
- ↑ Apitz, Kurt (September 1, 1935). "A Study of the Generalized Shwartzman Phenomenon". The Journal of Immunology. 29 (3): 255–266.
- ↑ Goswami R, Kochupillai N, Crock PA, Jaleel A, Gupta N (2002). "Pituitary autoimmunity in patients with Sheehan's syndrome". J. Clin. Endocrinol. Metab. 87 (9): 4137–41. doi:10.1210/jc.2001-020242. PMID 12213861.
- ↑ Abourawi, F (2006). "Diabetes Mellitus and Pregnancy". Libyan Journal of Medicine. 1 (1): 28–41. doi:10.4176/060617. ISSN 1993-2820.
- ↑ Atmaca H, Tanriverdi F, Gokce C, Unluhizarci K, Kelestimur F (2007). "Posterior pituitary function in Sheehan's syndrome". Eur. J. Endocrinol. 156 (5): 563–7. doi:10.1530/EJE-06-0727. PMID 17468192.