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Type I, II and III PPB
The PPB Registry believes that Type I, Type II, and Type III PPB are on a biologic continuum:
Type I PPB is a purely cystic lesion typically occurring in children under 2 years of age, median 10-11 months of age.
Type II PPB is a cystic and solid lesion occurring at median age 34 months.
Type III PPB is a completely solid lesion occurring at median age 44 months.
Progression of Type: In a given patient, the aggressiveness of PPB appears to progress over time when there is a recurrence. As discussed above, PPB Types I, II, and III occur, on average, in progressively older cohorts of children (see Basics of PPB, Age at Diagnosis). Among literature and Registry cases are several well-documented examples of Type I disease recurring as Type II and thereafter as Type III disease. In fact, Type I disease almost never recurs as Type I. In no case has PPB Type “regression” (III to II or II to I) been seen. (see Registry Publications Priest 2006)
Type Ir PPB
Since about 2006, PPB Registry pathologists have recognized a fourth “Type” of PPB called “Type Ir PPB” for “Type I-regressed PPB”. This is a cystic lesion similar to Type I PPB. It has a micro-architecture similar to Type I PPB with very delicate septa without malignant cells. There may be small spindle cells which are not primitive and foci of dystrophic calcification. It appears to be a lesion which has “regressed’ from an earlier Type I PPB or, alternatively, it is a genetically-determined lung cyst which did not evolve so far along a dysplastic path as to become malignant. Type Ir PPB was initially recognized in several members of families in which one or more relatives had frank PPB. Subsequently, Type Ir PPB has also been recognized in a few individuals with no known PPB relatives. Type Ir PPB may present with pneumothorax. It may exhibit large or small lung cysts and may be an incidental finding in a relative of a PPB patient. Type Ir PPB is recognized in individuals from childhood to adulthood. The cysts of Type Ir PPB are different from other lung cyst pathologies included in “congenital pulmonary airway malformation” (CPAM) or congenital cystic adenomatoid malformation (CCAM) categories. Pathologists encountering unusual lung cysts are encouraged to obtain consultation from PPB Registry pathologists at no cost. (See Registry Publications Hill 2008)
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