Pleura & peritoneum

• Ultrasound: multiloculated anechoic cysts (Curr Probl Cancer 2017;41:340, Obstet Gynecol Surv 2009;64:321)
• Computed tomography: multilocular low density, thin walled multicystic mass (Tumori 2008;94:14, Obstet Gynecol Surv 2009;64:321)
• MRI: multiple cysts - hypointense on T1, hyperintense on T2 (Clin Imaging 2017;42:133, Obstet Gynecol Surv 2009;64:321)

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• Approximately 50% experience peritoneal recurrence after debulking surgery (Cancer 1982;50:1615, Cancer 1989;64:1336)
• Recurrence free interval ranged from 1.7 - 21 (median, 8) years in one series (Cancer 1989;64:1336)
• Multiple recurrences common (Cancer 1989;64:1336, Hum Pathol 2003;34:369)
• High peritoneal carcinomatosis index and incomplete resection associated with increased recurrence risk (Cancer 1989;64:1336, Eur J Surg Oncol 2018;44:1100)
• Complete cytoreduction with hyperthermic intraperitoneal chemotherapy associated with reduced recurrence risk (21% at 10 years) (Eur J Surg Oncol 2018;44:1100)
• Death from disease extremely rare (Am J Surg Pathol 1988;12:737, Cancer 1989;64:1336, Hum Pathol 2003;34:369)
• Very rare cases present with or progress to epithelioid malignant mesothelioma (Am J Surg Pathol 1988;12:737, BMJ Case Rep 2014;2014:bcr2013200212, J Surg Oncol 2002;79:243)

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• Numerous small cysts lined by a single layer of bland, flat to cuboidal cells
• Delicate mesothelial papillae or buds may project into cyst lumina (Am J Surg Pathol 1988;12:737, Cancer 1989;64:1336)
• Cysts separated by scant loose to collagenous stromal septa
• No infiltrative invasion of underlying tissues (e.g., fat, bowel)
• Chronic inflammation and hemorrhage common
• Uncommon features (Am J Surg Pathol 1988;12:737)
  • Adenomatoid tumor-like foci
  • Squamous metaplasia of the mesothelial lining
  • Hobnail change of mesothelial lining
  • Brisk acute inflammation with mesothelial denudation and granulation type change
  • Small mesothelial nests, cords and single cells in lesional stroma; often associated with brisk inflammation
• Mesothelial nests, cords and single cells may be seen in stromal septa, often associated with brisk inflammation (termed mural mesothelial proliferation) (Cancer 1989;64:1336, Am J Surg Pathol 1986;10:844, Hum Pathol 2003;34:369)
  • Considered a superimposed reactive change
  • No diffuse sheet-like growth or infiltration of underlying tissues
• Recurrences histologically similar to primary lesions (Cancer 1982;50:1615, Cancer 1989;64:1336)

Contributed by David B. Chapel, M.D.

• Nonspecific sheets or strips of flattened or squamoid cells with distinct cell borders and small bland nuclei (Diagn Cytopathol 2010;38:192, Cytopathology 2008;19:224, Obstet Gynecol Surv 2009;64:321)

• Malignant mesothelioma:
  • Infiltrates underlying native tissues (e.g., fat, muscle, viscera)
  • Foci of expansile growth with tubulopapillary, papillary, glandular or solid architecture
  • Typically shows at least moderate atypia and mitotic activity
  • Approximately 80% will show BAP1 loss (IHC), CDKN2A deletion (FISH) or MTAP loss (IHC)
• Lymphangioma (Cancer 1982;50:1615, Am J Surg Pathol 1988;12:737, Hum Pathol 2003;34:369):
  • Unifocal lesion
  • Primarily seen in in retroperitoneum, mesentery or omentum
  • Uniform cyst size without intraluminal mesothelial budding
  • Endothelial lining positive for CD31, CD34, ERG
  • Negative for cytokeratin, calretinin, WT1

• Arch Gynecol Obstet 2018;297:1353

A 36 year old woman presents with pelvic discomfort, worsening over 6 months. Transvaginal ultrasound shows a multicystic lesion involving the cul de sac, left uterine adnexa and rectal serosa. The lesion is resected by laparoscopy. A representative H&E stained slide is shown. The cyst lining cells are positive for cytokeratin AE1 / AE3, calretinin and WT1 and negative for MOC31. The lesion is extensively sampled and no infiltrative growth is identified. Which of following is true?

1. Approximately 70% of such lesions harbor BAP1 mutations
2. Complex copy number alterations are characteristic of such lesions
3. Excision is curative; no clinical followup is required
4. Local recurrence affects approximately 50% of patients
5. Men are affected approximately four times as often as women

D. Local recurrence affects approximately 50% of patients. This is multicystic mesothelioma.

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Reference: Multicystic mesothelioma

Which of the following statements regarding multicystic mesothelioma is true?

1. 40 - 50% of lesions harbor homozygous deletion of CDKN2A
2. Approximately 20% of patients progress to malignant mesothelioma over 10 years
3. Destructive infiltration of underlying structures (e.g., omental fat) is seen in approximately 33% of cases and does not affect prognosis
4. Over 90% of lesions express estrogen receptor and progesterone receptor
5. Surgical excision is considered the mainstay of treatment

E. Surgical excision is considered the mainstay of treatment

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Reference: Multicystic mesothelioma